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DEPARTMENT OF AGRICULTURE PAPUA NEW GUINEA UNIVERSITY OF TECHNOLOGY

Niugini Agrisaiens

ISSN 1019-8407

Volume 2 Number 1 January- December 2010

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Niugini Agrisaiens

ISSN 1019-8407

PUBLISHED BY THE

DEPARTMENT OF AGRICULTURE, THE PAPUA NEW GUINEA UNIVERSITY OF TECHNOLOGY, PRIVATE MAIL BAG, LAE, 411, MOROBE PROVINCE, PAPUA NEW GUINEA, Phone: (+675) 4734451, Fax: (+675) 4734477,

Email: [email protected] or [email protected]

Technical Editors

Dr. Jayaprakash, PNG University of Technology

Dr. Maia Wamala, PNG University of Technology Dr. Peter Manus, PNG University of Technology

Mr. Macquin Maino, PNG University of Technology Assoc. Prof. S. Akoitai, PNG University of Technology

PUBLISHED ANNUALLY

Online version can be accessed at URL: http://www.unitech.ac.pg

© Department of Agriculture, Printed at Unitech Printery, Lae, Papua New Guinea

EDITORIAL BOARD Professor Abdul Halim, Editor-in- Chief

Dr. Rajashekhar Rao B.K., Executive Editor Professor Deirdre Lemerle, Charles Sturt University, Australia

Professor Biman Chand Prasad, University of South Pacific, Fiji Professor Yunus Musa, Hasanuddin University, Makassar, Indonesia

Dr. Thierry Mennesson, New Caledonian Agronomic Institute (IAC), New Caledonia Ms. Betty Tiko, Member Secretary, PNG University of Technology

mailto:[email protected]


http://www.unitech.ac.pg

Niugini Agrisaiens

1. Perception of participant women on social forestry program of Bangladesh Rural Advancement Committee

Sajia Afrin Khan Mojlish, M. Zulfikar Rahman, Suraia Akhter

1 - 8

2. Profitability of smallholder rice production in selected agro-ecological zones of Papua New Guinea

Peter A. Manus, Abdul Halim

9 - 16

3. Effect of late water stress on growth and tuber yield of nineteen sweet potato genotypes

Maia Wamala, Shamsul Akanda

17 - 25

4. A study on screening for resistance to vascular streak dieback in cocoa

James Butubu, Shamsul Akanda, Tom Okpul 26 - 29

5. Potential of newly bred sweet potato clones as improved cultivars under highland conditions of Papua New Guinea I. Performance of early maturing sweet potato clones

R. K. Kapila, B. Wera, M. Deros, S. Ivahupa, G. Bagle, T. Okpul, R. P. Pawilnga, E. Guaf

30 - 38

6. Potential of newly bred sweet potato clones as improved cultivars under highland conditions of Papua New Guinea II. Performance of orange flesh sweet potato clones

R. K. Kapila, B. Wera, M. Deros, S. Ivahupa, G. Bagle, T. Okpul, R. P. Pawilnga, E. Guaf

39 - 47

Volume 2, Number 1 January� December 2010

CONTENTS

Niugini Agrisaiens Research Article

Volume 2, 1� 8, 2010

PERCEPTION OF PARTICIPANT WOMEN ON SOCIAL FORESTRY PROGRAM OF BANGLADESH RURAL ADVANCEMENT

COMMITTEE Sajia Afrin Khan Mojlish, M. Zulfikar Rahman* and Suraia Akhter

Department of Agricultural Extension Education Bangladesh Agricultural University, Mymensingh, Bangladesh

ABSTRACT

A study was conducted to determine the perception of participant women on social forestry program of Bangladesh Rural Advancement Committee (BRAC) and to explore the relationship of the selected characteristics of the respondents with their perception of social forestry program. Seventy-five participant women of social forestry program of BRAC were randomly selected from Trishal upazila of Mymensingh district in Bangladesh. A pre-tested interview schedule was used to collect data from the respondents during August to September 2007. Most (59%) of the respondents had favorable perception while 30% and 11% of them had moderately favorable and unfavorable perception of social forestry program respectively. Respondents� education, training, duration of involvement in social forestry program, participation in social forestry program and knowledge of tree plantation had significant positive relationship with their perception of social forestry program except for age that had a significant negative correlation. Lack of required land, destruction of transplanted plant by severe storm, drought and flood, and social restriction on women to participate in social forestry program were the major constraints faced by women to participate in social forestry program. Creating awareness with the active involvement of local leaders about different aspects of social forestry is necessary to reduce the social restrictions on rural women to participate in social forestry programs.

Keywords: Perception, women, social forestry, BRAC

INTRODUCTION

Social forestry is a part of agriculture, which is the economic backbone of Bangladesh. According to

BBS (2006), forest resources contribute to the national GDP by about 22%. Social forestry is a forestry which

aims at ensuring economic, ecological and social benefits to the people, particularly to the rural masses and

those living below poverty line. Social forestry also aims at raising plantations by the common people so as to

meet the growing demand for timber, fuel wood, fodder, etc. thereby reducing the pressure on the traditional

forest area. The target of the social forestry is the �rural poor� and not the �tree� alone. This support, however, is not just to ensure that the trees get planted and survives but to ensure that the people who plant the trees receive

adequate sustenance to live with dignity before reaping the harvest from the raised crops.

Bangladesh Rural Advancement Committee (BRAC), based in Bangladesh, is currently (May 2010)

the world's largest non- governmental development organization. Established by Sir Fazle Hasan Abed in 1972

soon after the independence of Bangladesh, BRAC is currently present in all 64 districts of Bangladesh, with

over 7 million microfinance group members, 37,500 non-formal primary schools and more than 70,000 health

volunteers. BRAC is the largest NGO by number of staff employing over 120,000 people, the majority of whom

are women. BRAC operates various programs such as those in microfinance and education in over nine

countries across Asia and Africa, reaching more than 110 million people. The organization is 80% self-funded

through a number of commercial enterprises that include a dairy and food project and a chain of retail handicraft

stores called �Aarong�. BRAC maintains offices in 14 countries throughout the world, including ___________________________________________________________________________________________________ *Corresponding author: Tel: 880-1714-074313, FAX: 880-91-61510, Email: [email protected] Article received on 29th July, 2010; Accepted after revision on 15th September, 2010


BRAC USA and BRAC UK. BRAC is a few years into their initiative to operate in ten African countries in the next ten years (Wikipedia, 2010). The major objectives of BRAC are: a) Economic Development, b) Education, c) Public health, d) Social Development, and e) Disaster Relief. With the introduction of social forestry scheme, the government formally recognized the rights of local communities to forest resources and to encourage rural participant in the management of natural resources. Besides the government and other NGO initiatives, BRAC have been launching Social Forestry Program (SFP) since 1988 to increase awareness about the necessity of planting trees in rural areas, create a sustainable supply of high quality seedlings and reduce the adverse environmental effects of deforestation while creating income and employment opportunities for rural women. The Rural Development Program (RDP) was launched in 1986 with the approach of village organization (VO). The VOs organizes the poor, providing them with credit and other necessary technical support to make the optimum use of marginal land and other types of social forestry practice as Nursery (forest-fruit) establishment, Plantation and Agro-forestry. A pilot project on social forestry was launched under the Rural Enterprise Project (REP). The project initiated on private and government owned land in the northern district aiming to produce wood, fuel, fodder, food, fruit and vegetables. Farmers owning 0.35 to 0.50 ha of land were selected for the program. They were given a 3-day training as well as credit, seeds, technical support and follow-up services. BRAC aims to bring all available land in the rural areas (homestead, roadside, embankments, and marginal fallow) under tree cover with the active participation of the rural poor. The participants of the social forestry program are mostly rural women (BRAC, 2006). So, this study was conducted with the following objectives. 1. To determine the extent of participation of participant women in social forestry program of BRAC. 2. To determine the perception of participant women on social forestry program of BRAC. 3. To explore the relationships between perception of participant women on social forestry program of BRAC and their selected characteristics. 4. To identify the constraints faced by the participant women to participate in social forestry program of BRAC.

METHODOLOGY

The study was conducted in Trishal upazila of Mymensingh district in Bangladesh. Seventy five women out of a total 103 participant women were randomly selected from different villages of Trishal, Mothbari, Bailor, Balipara and Rampur unions to have the respondents of this study. Eventually, sample consisted of 73% of the sampling population. Data were collected from the women who had been participating in the social forestry program of BRAC.

Perception of social forestry program of the participant women was the dependent variable for this research. Participant women�s perception of social forestry program of BRAC was measured by considering the following three issues of social forestry program: 1. Management issues related to BRAC, 2. Economic issues and, 3. Environmental issues. A total of 22 statements were included in these issues for having a comprehensive view of the respondents regarding the perception of social forestry program. Five point Likert type scale was used for measuring the perception of social forestry program of BRAC. The scale was constructed with both positive and negative statements. Reverse scoring was done for negative statements (Rahman, 2000).

The total score of perception of Social Forestry Program (SFP) of a respondent woman was computed by summing her scores for all the 22 statements of three issues. Thus, the total scores of perception of a respondent could range from 22 to 110 where �22� indicated highly unfavorable perception and �110� indicated the highly favorable perception of social forestry program of BRAC. Effect of participation in the SFP by the women on other members of the society was also investigated by the researcher though it was not included in the specific objectives of the study. However, effect of

Niugini Agrisaiens 2, 1-8, 2010 Perception of women on social forestry Mojlish et al.

2

participation in the SFP by the women on other members of the society was also investigated by the researcher though it was not included in the specific objectives of the study. However, effect of participation in social forestry program on other members of the society was measured in terms of extent to which other social members had become motivated from the respondent�s participation in social forestry program of BRAC. Five types of social members were considered in this case, such as other family members, neighbors, friends, relatives and others. Four- point rating scale was used to determine the extent of effect. Scores were assigned as �0� for �not at all�, �1� for �low�, �2� for �medium� and �3� for high extent of effect. Finally, sum of the scores of effect on all social members was considered as the total score of effect of participation in social forestry program. The scores of effect of participation in social forestry program of BRAC could range from 0 to 15. Constraints faced by the women to participate in social forestry program of BRAC was measured by using closed form questions. The women were asked to give their opinion on 10 selected constraints to participate in social forestry program of BRAC. A four point rating scale was used for computing the constraint score of a respondent. For each constraint, score of �3�, �2�, �1� and �0� was assigned to indicate extent of constraint as �high�, �medium�, �low� and �not at all� respectively. The total constraint scores were computed for each respondent by adding her scores for all the problems. The possible range scores of constraints could be 0 to 30 where a total score of �0� indicated no constraints in respect to participate in social forestry program of BRAC while a score of �30� indicated highest extent of constraints. To ascertain the comparison among the constraints, Constraint Facing Index (CFI) was computed using the following formula which was used by Afique (2006): CFI = (Ph ´ 3) + (Pm ´2) + (Pl ´ 1) + (Pn ´ 0) Where, CFI = Constraint facing index Ph = Number of respondents having high constraint Pm = Number of respondents having medium constraint Pl = Number of respondents having low constraint Pn = Number of respondents having no constraint at all

At the end of the interview, the respondents were requested to give their suggestions to overcome the constraints to participate in social forestry program of BRAC. In order to collect data from the participant women of social forestry program of BRAC, a structured interview schedule was used. Descriptive statistical tests such as number, percentage distribution, range and standard deviation were used. Pearson�s Product Moment Correlation Coefficient (r) was computed to explore the relationships between dependent and independent variables (Ray and Mondal, 2004).

RESULTS AND DISCUSSION

Perception of Social Forestry Program of BRAC

The main thrust of this study was to determine how the participant women perceived social forestry program of BRAC. The total possible scores could range from 22 to 110 but the obtained scores by the respondents ranged from 44 to 105 (Table 1). According to the scale value, the respondents were classified into three categories. The highest proportion (58.66%) of the participant women had favorable perception while 30.67% and 10.67% of them had moderately favorable and unfavorable perception of social forestry program, respectively.


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Table 1. Distribution of participant women according to their percep-tion of social forestry program of BRAC

Respondents Mean

score Std. Dev.

Category regarding perception No. %

Unfavorable (≤49)

Moderately favorable (50-77)

Favorable (>77)

8

23

44

10.67

30.67

58.66

78.92 16.794

Table 2. Perception of participant women on different issues of social forestry

Issues of social forestry

Range of score Respondents Mean score

Std. Dev. Possible Observed Category No. %

Management 8-40 10-38 Unfavorable (≤18) Moderately fav. (19-29) Favorable (>29)

7 25 43

9.33 33.33 57.34

28.45 5.92

Economic 8-40 13-36 Unfavorable (≤18) Moderately fav. (19-29) Favorable (>29)

5 21 49

6.67 28.00 65.33

29.37 6.75

Environmental 6-30 10-30 Unfavorable (≤14) Moderately fav. (15-22) Favorable (>22)

7 26 42

9.33 34.67 56.00

21.09 4.97

Table 3. Relationships between the dependent and independent variables

Dependent variable Independent variables Correlation coefficient

�r� with 73 d.f.

Perception of social forestry program of BRAC

Age -0.353** Education 0.245*

Family size -0.155 Farm size 0.071 Annual family income -0.190

Training experience 0.253*

Extension media contact 0.213

Duration of involvement in SFP 0.348**

Participation in SFP 0.338** Knowledge on tree plantation 0.314**

** Significant at 1% level of probability * Significant at 5% level of probability


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Training experience and level of education of the participants helped them to secure proper knowledge on social forestry program of BRAC. Moreover, they had built up a favorable perception of social forestry program from their active participation in the program of social forestry. Consequently, most of the respondents possessed favorable perception of social forestry program of BRAC. More detail information regarding perception of social forestry program of the participant women have been presented in Table 2.

Among the respondents, 65.33% had favorable perception of social forestry program regarding economic issues while 57.34% and 56% had favorable perception in case of management and environmental issues of social forestry program. This meant that they were relatively more aware of economic issues followed by management issues related to BRAC. On the other hand, the average score (29.37) of economic issues was the highest among the three issues of social forestry in connection with the observed range for these issues. However, coefficients of variation were 20.81%, 22.98% and 23.58% for management, economic and environmental issues respectively. That is similar extent of variation existed among the respondents regarding these issues of social forestry program of BRAC.

Relationships between dependent and independent variables

Table 3 indicated that age of the respondents had significant negative relationship with their perception of social forestry program. In another Bangladeshi study, Biswas (2009) also found similar finding that rural women�s perception of prospect of scavenging chicken rearing was significantly related to their age. Finding of Alam (2008) is also supportive to this one. Older women are less assertive about the necessity of forestry and to plant more trees as they were, in general, less aware of critical issues of environmental issues. Maybe, for this reason, older women did not perceive favorably of social forestry program of BRAC. Education and perception of social forestry program showed significant relationship. Sharmin (2005) and Sayeed (2002) also found similar findings in their studies. Education increases knowledge and changes attitude. It increases one�s power of observation, understanding, decision-making ability and adjustment to new situation. Educated persons are more aware about any social issue. Therefore, women being higher educated perceived more perception about forestry program.

The relationship between training experience of the women and their perception of social forestry program was significant. Kabir (2002) also found similar result. Training is the process of increasing one�s skill, knowledge and attitude. Training makes a person more confident and helps to develop more favorable attitude to the social issues. So, women having higher training experience might have more perception about social forestry program. Duration of the social forestry program and women�s perception about it was significantly correlated. Short term programs help a person to be initially benefited but long term programs help ones to acquire deep knowledge about any subject. With the increase of the duration of any program the chance of knowing about that program also increased.

Participation in SFP showed significant relationship with the perception of women about it. Afique (2006)

also found similar relationship in his study. Participation in any program brings a person closer to that program. Coming into the program persons get chance to know more and get scope to share their knowledge with one another that helps them to be more assertive. Therefore, women being participated into social forestry program should develop more perception. Knowledge on tree plantation was significantly correlated with women�s perception in social forestry program. Sayeed (2002) also found the same results in his study. Knowledge about any subject matter increases ones thinking capability and makes the person more assertive of that subject. So, women with high knowledge on tree plantation might have better perception about social forestry program.

Effect of participation in SFP on other social members

Findings indicate that the observed scores of effect of participation ranged from 2 to 10 against a possible range of 0 to 15. Among the respondents, 56% opined that the other social members were motivated to a moderate extent due to the participation of the respondent women while 44% agreed on the low extent of effect on the other social member of the society in this context. The rural women in general are less cosmopolite in nature. Moreover, the rural people normally manage their homestead trees for fruits, timber and so on. They are inherently careful about tree plantation. Therefore, none of the respondent women agreed that the other social member became motivated to a great extent for tree plantation solely from their participation in social forestry program of BRAC.


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Table 5. Categories of women according to constraints faced to participate

Respondents Mean

score

Std.

Dev. CV

Category No. %

Low (≤10)

Medium (11-20)

High (>20)

43

32

0

57.33

42.67

0

10.33 2.703 26.17

Table 4. Effect of participation in SFP by other members of the society

Respondents Mean score

Std. Dev.

CV Category No. %

Low (≤5) Medium (6-10) High (>10)

33 42 0

44 56 0

5.95 1.944 32.67

Constraints to participate in social forestry program Total observed scores of constraints ranged from 6 to 17 against the possible range of 0 to 30. The

average was 10.33 and standard deviation 2.703 as shown in Table 5. Data presented in Table 5 indicated that the majority (57.33%) of the respondents faced low extent of problems while the rest 42.67% of them faced moderate extent of problems to participate in social forestry program of BRAC. The extent of constraints to participate in social forestry program in terms of Constraint Facing Index (CFI) along with their rank order based on the CFI values have been presented in Table 6.

Data indicate that the constraint which ranked first was �lack of required land� which was the most crucial problem faced by the participant women in participating social forestry program. It was a real situa-tion of the study area because there was not enough land for social forestry program. Some of the respon-dents were afraid to participate due to risky climatic condition. There was a possibility of destruction of transplanted young plants by storm, drought and flood. Besides, these major problems, some minor but im-portant problems also restricted the respondents to participate in social forestry program, such as social and religious restriction on women to participation in social forestry program, destruction of plants by cattle and others, very tough to save tree from insects etc.

Table 6. Ranking of the constraints according to descending order of CFI

Constraints CFI Rank order

Lack of required land 162 1 Destruction of transplanted plant by excessive storm, drought and flood 128 2 Problem of plantation in low land 93 3 Social restriction on women to participate in SFP 69 4 Destruction of plants by cattle and others 67 5 Very tough to save tree from insects 67 6 Complexity in sharing trees of social forestry 63 7 Religious restriction on women to participate in SFP 62 8 Negative attitude and obstacles from local leader 49 9 Mature trees are stolen by thief 15 10


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Finally, the respondents were also requested to express their opinions on how these constraints could be overcome. The following opinions were given by the respondent women in order to solve their constraints:

Allocation of Government khash (reserved) lands for the rural women so that they can use the lands for

social forestry.

Introduction of tree species which can be grown in low land under water logging condition for few months

a year.

Creating awareness with the active involvement of local leaders about different aspects of social forestry in

order to reduce the social and religious restriction on the rural women.

Supply of adequate pesticides by the concerned organizations for the protection of trees from insect pests

and diseases.

Formulating and monitoring proper rules for sharing profits among the participants.

Conclusion

The highest proportion of the respondents had favorable perception of social forestry program and there were some respondents who possessed unfavorable perception of social forestry program of BRAC. So, there was a scope to take necessary steps to make them aware of the importance of social forestry which would help them to perceive well about the benefits of social forestry. Among the respondents more than half were young and the young women had more favorable perception of social forestry program and they could functionally participate in social forestry program to materialize the objectives of social forestry. Education levels of the respodents were highly influential for the formation of favorable perception of social forestry program of BRAC. So, educational facilities have to be availed for the adult rural women through government and non-government initiatives in order to improve knowledge on environment as well as social forestry. Most (76 %) of the women had short-term training experience which had significant relationship with the perception of social forestry program. So, arrangement for effective training program is urgent for the women to develop their skills and knowledge on social forestry by the concerned organizations. Longer duration of involvement in social forestry program helped the participants to make favorable perception of social forestry program. Government should allocate the khash (reserved) lands for the rural women so that they can use the lands for social forestry. There is a need to create social awareness with the active involvement of local leaders about different aspects of social forestry in order to reduce the social and religious restriction on the rural women to participate in social forestry.

REFERENCES

Afique, A.A. (2006). Rural women�s perception of benefit from agricultural model farm project of SUS. M.S. (Ag.

Ext. Ed.) Thesis, Dept. of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

Alam, N. (2008). Framers� perception of soil quality degradation due to less use of organic matter. M.S. (Ag. Ext.

Ed.) Thesis, Dept. of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

BBS. (2006). Statistical year book of Bangladesh. Bangladesh Bureau of Statistics, Ministry of Planning, Government of the People�s Republic of Bangladesh, Dhaka.

Biswas, M. (2009). Rural women�s perception of prospect of scavenging chicken rearing. M.S. (Ag.Ext.Ed.) Thesis, Department of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

BRAC. (2006). Overview: economic development. Bangladesh Rural Advancement Committee. <http://www.brac.net/usa/bw_economic_development.php>


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http://www.brac.net/usa/bw_economic_development.php

Kabir, M.T.N. (2002). Perception of farmers on the effects of Barind Integrated Area Development Project towards environmental upgradation. M.S. (Ag.Ext.Ed.) Thesis, Department of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

Rahman, M.Z. (2000). Farmers� perception of sustainable agricultural development. Doctoral Thesis. Graduate School of Biosphere Science, Hiroshima University, Hiroshima

Ray, G.L. and Mondal S. (2004). Research methods in social sciences and extension education. New Delhi: Kalyani Publishers.

Sayeed, M.A. (2002). Farmers� perception of benefit from using manure towards Integrated Nutrient Management (INM) for sustainable crop production. M.S. (Ag.Ext.Ed.) Thesis, Department of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

Sharmin, H. (2005). Rural women�s perception of benefits of involvement in Income Generating Activities under a Non-Government Organization. M.S. (Ag.Ext.Ed.) Thesis, Department of Agricultural Extension Education, Bangladesh Agricultural University, Mymensingh.

Wikipedia. (2010). BRAC (NGO). Found at [http://en.wikipedia.org/wiki/BRAC_(NGO)].


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Volume 2, 9� 16, 2010


PROFITABILITY OF SMALLHOLDER RICE PRODUCTION IN SELECTED AGRO-ECOLOGICAL ZONES OF PAPUA NEW GUINEA

Peter A. Manus* and Abdul Halim

Department of Agriculture, PNG University of Technology,

Private Mail Bag, Lae 411, Papua New Guinea

ABSTRACT

Agricultural policy of Papua New Guinea focuses on the national food security and the debate on how to attain it. Rice, although not an important food crop in the diverse farming systems practices, it has firmly emerged as a staple food in PNG. Its importance is reflected in the amount of rice imported,150,000 metric tons, and amount of PNG Kina spent on rice imports, PNG K216 million, per annum. Due to the weaker PNG Kina, the retail price of rice has increased to 120 percent, between 1994 and 2003,. Because of the increased burden of financing rice imports, the government has encouraged rice self-sufficiency since 1998. The strategy was to promote domestic rice production as a smallholder industry. This study, which was conducted in the highlands, wet lowlands and dry lowlands agro zones, aimed at evaluating financial profitability of rice production systems in these agro zones. The data were generated from multi location rice varietal performance trials conducted in these agro zones. The analysis was modeled on smallholder rice farming with low input- low output situation. The results indicate that smallholder farmers make minimal fixed capital investments and cash cost inputs. Family labor was found to be the single most important input in smallholder rice production. All rice production systems were found to be financially profitable with net returns per man-days of labor greater than the rural minimum wages rate. Furthermore, milled rice was found to be more profitable than paddy rice.

Key words: smallholder, multi location rice varietal trials, farm investment, input-output valuation, farm returns

INTRODUCTION

During the past decade, an agenda that received a lot of attention in the Papua New Guinea (PNG) agricultural policy was on the national food security, and the debate on how to attain it. Among the various forces that made the country vulnerable to food security were the natural disasters, the most severe has been the 1997/98 drought, which caused wide spread food shortages, leading to food mobilization nationally and internationally. The food which featured prominently in the national food relief program was rice. During the post war period since 1935, rice emerged strongly and consequently has now become prominent in the PNG food basket. Presently, rice imports amount to 150,000 tonnes per annum. In retrospect, it can be adduced that rice demand in PNG was high and has been increasing over the post war period. The increasing annual rice imports could be reflective of its demand growth over that period. For instance, from 1994 to 1998, the amount of rice imported grew at 6 per cent per annum. Essentially then, rice contributes a significant part to the national nutrition and calorie requirements, thereby playing a critical role in the national food security. Rice is however, not an important crop in the varied production systems practiced in PNG, except in the Finschafen area. Furthermore, rice has been grown only in few places; for example, Finschafen,

____________________________________________________________________________________________ *Corresponding author: Tel: (675)-4734451, FAX: (675)-4734477, Email: [email protected] Article received on the 9th July, 2010; Accepted after revisions on the 18th November, 2010


Maprik, Berenia, Badu and Nuku and mostly by smallholder farmers in those areas. Given the low level of attention, local production meets only 10 per cent of total rice supply in the country (Akter, 2003). Consequently, the country is spending a considerable amount of foreign exchange to import rice, which is likely to increase with demand and/or population growth or both. Recent rice import spending estimates amount to PNGK 216 million per annum (DAL, 2004). In the 1994 and 1996 period, the Australian government�s support to PNG government has been progressively withdrawn. Government spending has since been financed principally from domestic borrowing causing inflation, long-term decline in the value of the Kina, and negative real growth in GDP (Akter, 2003). These outcomes were, in large part, the Government�s stance on moving away from aid dependency syndrome. During the same period, the government intervened in the foreign exchange market and has switched from a fixed exchange rate regime to the floating exchange regime. The outcome of this macroeconomic policy is the devaluation of the PNG Kina which further caused inflation and a decline in the value of the PNG Kina. For example, the depreciation of the Kina has reduced its value from US$ 0.85 per Kina in 1994 to US$0.24 per Kina in 2003. This had caused an increase in the retail price of imported rice by about 120% (DAL, 2004). Given this situation, it may not be justified to meet the huge demand of rice from import only. The foregoing sections highlighted two significant features that could help to generate serious thought to increase local rice production. First, rice has become a staple in PNG. Consequently rice imports have been increasing due to increases in consumption and increases in the population growth. However, due to the decline in the value of the Kina, there is a huge burden for PNG in financing the huge demand of rice from imports. The national position now has become, although challenging, is to secure food security with emphasis on rice self-sufficiency. The policy focuses on sequential savings from rice imports and thereby reducing the burden of financing rice imports. It is argued that these national strategic concerns are, in the long term, realizable given the favorable agronomic and climatic conditions, similar to the neighboring rice growing countries of Indonesia and the Philippines. The self-sufficiency strategy advocated was to popularize rice production as a smallholder industry, both for home consumption and as an alternative cash crop. All that is yet to be done is to identify an appropriate and responsible policy intervention strategy. In the past two decades, when the rice self-sufficiency policy was seriously mooted, Gibson (1994) argued that Papua New Guinea (PNG) would be better off (by 2.9% in its balance of trade) if she concentrated on producing the export tree crops, which she has comparative advantage and exchange these crops for rice. The argument was advanced based on the premise that PNG would not deliver rice at prices equivalent to and/or lower than the prevailing world market prices, an argument supported by Blakeney and Clough (2000). It must be, however, noted that at the time Gibson (1994) advanced these arguments the PNG currency was strong and in par with the US dollar. In this context, promoting rice based farming systems in PNG is justified not on the efficiency ground but on the difficulties of meeting the rice import bill and food security considerations. While these issues are of national concerns, which require answers to be provided, at the farm level, rice production must be profitable and has returns to labor that are higher than the prevailing rural minimum wages rate. This study was conducted to assess the competitiveness of rice production systems in three agro-ecological zones; the wet lowlands, dry lowlands and the highlands agro- ecological zones. Competitiveness of a rice production system has been assessed using the enterprise net financial profitability.

MATERIALS AND METHODS Study Locations The study on the costs and returns of rice production systems was undertaken at three agro-ecological zones. They were the Unitech Farm of Morobe Province which represented the wet lowlands agro-ecological

Niugini Agrisaiens 2, 9-16, 2010 Profitability of rice in agro -ecological zones Manus and Halim

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zone; the Clean Water Farm in the Markham Valley of Morobe Province represented the dry lowlands agro-ecological zone and the Kabiufa Farm of Eastern Highlands Province represented the highlands agro zone. Unitech Farm is situated at the PNG University of Technology, Taraka Campus while the Clean Water Farm is situated in the Markham Valley and was managed by the Trukai Industries. The Kabiufa Farm was located at Kabiufa High School. In each study site several rice varieties have been trialed for their yield performances. The input and output requirements of each variety may vary. Consequently, each of the production technologies can be described as separate production systems. Measurement Points Farm level profitability models were developed for each of the rice farming systems using activity budgeting (Gittinger, 1982). The measurement of competitiveness of each production system can be made at three points distinguished by production, processing and marketing arrangements. The first is at the farm gate covering production only. This is where it is assumed that rice, produced from the different agricultural zones, is disposed in un-milled form to processors. The second measuring point is at the village gate covering production, processing and marketing. This is where it is assumed that un-milled rice is taken home, dried and winnowed and then processed using mini-mills available in the village. The farmers then disposed the milled rice to buyers in the villages of producing sites and to Trukai Industries for farmers who live closer to its processing facilities. For the purpose of this study, paddy was assumed to be sold to processors and milled rice to consumers within the rice producing sites. These appeared to be reasonable assumptions given the small amount of rice produced by farmers, although Trukai Industries do buy both paddy and milled rice from the producing sites in Morobe Province. It must be noted that rice is a potential competitor for other cash generating activities, for instance among others, coffee in the Highlands region and Peanut in the Low Drylands of Morobe Province. Ideally, competitiveness and comparative advantages of these competitors must be assessed. This is not possible since this study uses experimental data to model smallholder rice farmer situations.

Valuation of Inputs and Outputs Financial budgets were prepared for each of the rice farming systems studied. The financial budgets were prepared to estimate the financial profitability, which accrued to the private farmer. The data required for constructing these budgets were yields, input requirements, and the outputs. Inputs constitute cash cost inputs and non-cash cost inputs. An example of the later is family labor. The inputs and outputs were valued at their market prices. Family labor was valued by using the rural minimum wages rate of K3.95. Since no land markets exist in the rural sector, land was valued at its opportunity cost, the net return to peanut production which was for the purpose of this study assumed be the next best alternative economic smallholder crop. For example, in the highlands, the next best alternative is coffee but no net return to smallholder coffee is available. In general, the non cash inputs were valued at their opportunity costs.

Types and Sources of Data The data collected can be divided into primary and secondary data. The primary data can further be divided into experimental data and farm data. The experimental data constituted the input-output data generated from the multi-location rice varietal performance trials conducted at Unitech Farm, Trukai Clean Water Farm and NARI Kabiufa farm. The trials at Unitech Farm and Trukai Clean Water Farm were conducted from 2001 to 2003 under a Trukai-Unitech Collaborative Rice Research Project funded by the Trukai Rice Industries. The trials at Kabiufa were conducted by NARI also funded by Trukai Rice Industries during the same period. These data formed the basis for the costs of production and profitability analysis of the rice farming systems studied. The secondary data required for this study were the market or financial prices of the inputs


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and outputs. These information were obtained from various publications from the Departments of Agriculture and Livestock, Trade and Industry, National Planning, Bank of PNG, Bureau of National Statistics, and PNG Internal Revenue Commission. Sample size of the experimental data constitute input-output data from all rice varietal trials conducted in the named locations between 2001 and 2005. The varieties selected for the study were the ones commonly grown in the study sites.

Methods of Data Collection and Analysis The data were collected from the rice varietal trial records and publications from National Agricultural Research Institute (NARI), UNITECH and TRUKAI Rice Industries who conducted the location varietal trials. The data collected were the input-output data and the relative prices of the inputs and outputs. The data collected were analyzed by using the cost accounting approach. This approach is used to account for costs, revenue and profits. Essentially, the approach is used to calculate the net financial profitability (NP) which can be defined as the difference between total revenue (TR) and total cost (TC). That is, NP = TR � TC, where TC constitute fixed and variable costs. The rice production systems were distinguished by location and variety. The input-output coefficients were, for the purpose of analysis, converted to per hectare basis. Furthermore, the analysis was modeled on smallholder farming with low input � low output as baseline situations.

RESULTS AND DISCUSSION Cost Structure of Rice Production The costs of rice production can be categorized into fixed costs and variable costs. These costs can further be decomposed into cash costs and non-cash costs of production. The latter categorization of costs of production is necessary in order to identify not only the most important costs components where smallholder farmers operate on a less cash cost input situation but bottle necks where non-cash cost inputs predominate production. Fixed costs constitute the costs for farm tools, seeds and drying canvas while variable costs constitute operating costs which are the costs of fertilizers, weedicides, sacks, processing and interest on capital and imputed costs of family labor. Non-cash costs constitute the monetary value of family labor for the different farm activities performed during the cropping season. Family labor was imputed at K3.95, the prevailing rural minimum wages rate per man-day of labor. A man-day is defined as the amount of work done by an able bodied human being in 8 hours. The costs of production for all rice production systems for a given agro zone were found to be the same. This was due to incurring the same amount of cash and non-cash cost inputs for all rice varieties except for interest on capital, sacks and milling, which varied. The variation in the milling and sacks costs reflect the differences in yields obtained from the rice varieties in the given study sites. The summary estimates of the costs of paddy and milled rice production systems are discussed below.

Cost Composition of Paddy and Milled Rice Production Systems Tables 1 and 2 provide the summary estimates of the cost composition for paddy and milled rice production systems by agro-ecological zones. Total variable costs, for all paddy production systems, amount to about 92 percent of total costs at Unitech Farm, about 91 percent at Clean Water Farm, and 91 percent at Kabiufa Farm while for milled production systems, it amount to about 94 percent of total costs at Unitech Farm, about 94 percent at Clean Water Farm, and 93 percent at Kabiufa Farm. Essentially then, variable costs have been found to be the most important costs of paddy and milled rice production in all study locations.


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Table 1. Summary estimates of cost composition for paddy rice production systems by agro ecological zones ______________________________________________________________________________ Agro zones/ Fixed costs Variable costs Total variable Total costs production (Kina/ha) _________________ costs (Kina/ha) (Kina/ha)

UNITECH FARM TSC 10 146.00 462.99 1,208.70 1,671.69 1,817.69 (8.03)* (25.47) (66.50) (91.97) (100) Finsch 146.00 451.99 1,208.70 1,660.69 1,806.69 (8.08) (25.02) (66.90) (91.92) (100) IR19661 146.00 455.29 1,208.70 1,663.99 1,809.99 (8.07) (25.15) (66.78) (91.93) (100) CLEAN WATER TSC 10 155.00 503.69 1,054.65 1,558.34 1,713.34 (9.05) (29.40) (61.55) (90.95) (100) Finsch 155.00 480.59 1,054.65 1,535.24 1,690.24 (9.17) (28.43) (62.40) (90.83) (100) IR19661 155.00 505.56 1,054.65 1,560.21 1,715.21 (9.04) (29.48) (61.49) (90.96) (100) KABIUFA TSC 10 166.00 570.90 1,030.95 1,601.85 1,767.85 (9.39) (32.29) (58.32) (90.61) (100) IR19661 166.00 581.90 1,030.95 1,612.85 1,778.85 (9.33) (32.71) (57.96) (90.67) (100) Golden Mt 166.00 575.30 1,030.95 1,606.25 1,772.25 (9.37) (32.46) (58.17) (90.63) (100) _____________________________________________________________________________

technologies Operating Labor costs/ha costs/ha

Of the variable costs, the imputed costs of labor for paddy production systems constitute about 67 percent, 62 percent and 58 percent of total cost for the Unitech, Clean Water, and Kabiufa Farms respectively while for the milled rice production systems, it amount to about 48 percent, 36 percent and 41 percent of total cost for the Unitech, Clean Water, and Kabiufa Farms respectively. Essentially, the imputed value of labor was found to be the most important variable cost for paddy and milled rice production systems in all agro-ecological zones. Fixed costs of production for paddy productions systems amounted to about 8, 9 and 9 percent of total costs of production for the Unitech, Clean Water and Kabiufa Farms respectively while for the milled rice production systems, it amounted to about 6, 5 and 7 percent of total costs of production for the Unitech, Clean Water and Kabiufa Farms respectively. These results reflect that smallholder farmers incur very minimal fixed capital investments for rice farming.

Profitability of Rice Production

Farm level financial budgets were developed for each Unitech, Clean Water, and Kabiufa rice production systems. This was done to provide the database for establishing the relative profitability of rice production systems in each agro-ecological zone. The private profitability indicators show the incentives, foe each production system, to alter the existing allocation of resources. If private profitability is positive, resources are channeled to flow into the production systems. If private profitability is, on the other hand negative, the flow of resources will be moved away from the activity to more profitable production systems.

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Table 2. Summary estimates of cost composition for milled rice production systems by agro-ecological zones ____________________________________________________________________________ Agro zones/ Fixed costs Variable costs Total variable Total costs production (Kina/ha) __________________ costs (Kina/ha) (Kina/ha)

UNITECH FARM TSC 10 146.00 1,285.67 1,208.70 2,494.37 2,640.37 (5.53)* (48.69) (45.78) (94.47) (100) Finsch 146.00 1,125.37 1,208.70 2,334.07 2,480.07 (5.89) (45.38) (48.74) (94.11) (100) IR19661 146.00 1,173.34 1,208.70 2,382.04 2,528.04 (5.78) (46.41) (47.81) (94.22) (100) CLEAN WATER TSC 10 155.00 1,825.34 1,054.65 2,879.99 3,034.99 (5.11) (60.14) (34.75) (94.89) (100) Finsch 155.00 1,506.95 1,054.65 2,561.60 2,716.60 (5.71) (55.47) (38.82) (94.29) (100) IR19661 155.00 1,860.00 1,054.65 2,914.65 3,069.65 (5.05) (60.59) (34.36) (94.95) (100) KABIUFA TSC 10 166.00 1,239.90 1,030.95 2,270.85 2,436.85 (6.81) (50.88) (42.31) (93.19) (100) IR19661 166.00 1,387.10 1,030.95 2,418.05 2,584.05 (6.42) (53.68) (39.90) (93.58) (100) Golden Mt 166.00 1,295.51 1,030.95 2,326.46 2,492.46 (6.66) (51.98) (41.36) (93.33) (100) ___________________________________________________________________________ * Figures in the parentheses are percentages of total costs of production.

The producers have 3 rice marketing alternatives. The first was to sell rice as paddy to Trukai Industries at K0.80 per kilogram. The alternative to selling rice as paddy was to mill the paddy and sell it in milled form. The milled rice can be sold to the Trukai Industries or to villages at the producing and milling sites at K2.00 per kilogram. All of these marketing alternatives were analyzed. Tables 3 and 4 present the summary estimates of the financial farm budget indicators for paddy and milled rice production systems for all agro-ecological zones respectively. When rice was sold in paddy form (Table 3), the production systems of all the agro-ecological zones generated positive profits with the net returns man-day of labor greater than the prevailing rural minimum wages rate of K3.95. At the Unitech Farm the variety TSC 10 generated the most profit (K726.31) with a net return per man-day of labor of 1.5 times greater than the rural minimum wages rate of K3.95. At the Clean Water Farm, the production systems IR19661 and TSC 10, in that order, generated the most profits (K2, 696.79 and K2, 586.66) with net returns per man-day labor of 3.5 times greater than the prevailing rural minimum wages rate of K3.95. At the Kabiufa Farm, the Variety IR19661 generated the most profit (K721.15) with a net return per man-day of labor of 1.5 times greater than the rural minimum wages rate of K3.95. When rice was sold in milled form and at price K2.00 per kilogram (Table 4), all production systems were making profits with net returns per man-day of labor 1.5 to 4 times greater than the prevailing rural minimum wages rate of K3.95. At the Unitech Farm, TSC 10 generated the most profit (K1, 752.23) with a net return per man-day of labor of 2.5 times greater than the rural minimum wages rate of K3.95. At Clean Water

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technologies Operating Labor costs/ha costs/ha

_________________________________________________________________________ Agro zones/ Net returns to Net returns Total production Net production family labor per manday of costs enterprise

UNITECH FARM TSC 10 1,935.01 6.32 2,117.69 726.31 Finsch 1,438.01 4.70 2,106.69 229.31 IR19661 1,590.71 5.19 2,109.99 382.01 CLEAN WATER TSC 10 3,641.31 13.64 2,013.34 2,586.66 Finsch 2,640.41 9.89 1,990.24 1,585.76 IR19661 3,751.44 14.05 2,015.21 2,696.79 KABIUFA TSC 10 1,291.11 4.95 2,067.85 260.15 IR19661 1,752.10 6.71 2,078.85 721.15 Golden Mt 1,462.70 5.60 2,072.25 431.75 _________________________________________________________________________

Table 3. Summary estimates of financial farm budget indicators for paddy rice production systems by agro-ecological zones

technologies per ha (Kina) labor (Kina) (Kina/ha) profit/ha

_________________________________________________________________________ Agro Zones/ Net returns to Net returns Total production Net production family labor per manday of costs enterprise

UNITECH FARM TSC 10 2,960.93 9.68 2,940.37 1,752.23 Finsch 2,283.03 7.46 2,780.07 1,074.33 IR19661 2,492.46 8.15 2,828.04 1,283.76 CLEAN WATER TSC 10 5,309.66 19.89 3,334.99 4,255.01 Finsch 3,938.45 14.75 3,016.60 2,883.80 IR19661 5,459.80 20.45 3,369.65 4,405.15 KABIUFA TSC 10 2,135.30 8.18 2,736.85 1,104.35 IR19661 2,406.90 9.22 2,884.05 1,375.95 Golden Mt 2,370.09 9.08 2,792.46 1,339.14 _________________________________________________________________________

Table 4. Summary estimates of financial farm budget indicators for milled rice production systems by agro-ecological zones (Sold at K2.00)

technologies per ha (Kina) labor (Kina) (Kina/Ha) profit/ha

Farm, the production system IR19661 was found to be most profitable (K4,405.15) followed by TSC 10 (K4,255.01) with net returns per man-day of labor 5 times greater than the rural minimum wages rate of K3.95. At the Kabiufa Farm, the production system IR19661 generated the most profit (K1,375.95) with net return per man-day of labor 2 times greater than the rural minimum wages rate of K3.95.

Conclusions From the forgoing analysis the following surface: that smallholder farmers make minimal fixed capital investments and minimal variable cash cost in rice production. Family labor remains the most important non-cash cost input in smallholder rice production. Essentially, rice farming is labor intensive and therefore labor

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saving technologies must be found. Nevertheless, smallholder rice production appears to be profitable and has returns higher than the prevailing rural minimum wages rate. The analysis on the net returns of the paddy and milled rice production systems indicate that the production systems TSC 10, TSC 10 and IR19661 and IR19661 were the most important production technologies for the Unitech, Clean Water and Kabiufa Farms respectively. Essentially, they are the varieties to be grown in those study sites. However, milled rice production systems were found to be more profitable than paddy production systems. Given these outcomes, it is most profitable for farmers to mill rice and sells it either to the Trukai Industries or in the local villages at K2.00 per kilogram. They can only sell it to the Trukai Industries in paddy form if they can not have access to milling services in the study sites.

REFERENCES

Akter, S. (2003). Competitiveness of rice production in Papua New Guinea. In Trukai-Unitech collaborative

rice research project proposal. Department of Agriculture, Papua New Guinea: Unitech. Blakeney, M. and Clough, R. (2000). An assessment of grain production and imports in PNG, In Proceedings of the Papua New Guinea Food and Nutrition 2000 Conference, 23-29 (Ed R. M. Bourke, M.G. Allen and J. C. Salisbury), UNITECH, LAE, June 26-30, 2000, ACIAR Proceeding No. 99. DAL (2004). White Paper on Agriculture, Department of Agriculture and Livestock, Konedobu, Papua New Guinea. Gibson (1994). Rice self-sufficiency in Papua New Guinea. Review of Marketing and Agricultural

Economics, 62: 63-77. Gittinger, J.P. (1982). Economic Analysis of Agricultural Projects, 2nd Edition. Baltimore: John Hopkins University Press.

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Volume 2, 17� 25, 2010


EFFECT OF LATE WATER STRESS ON GROWTH AND TUBER YIELD OF NINETEEN SWEET POTATO GENOTYPES

Maia Wamala and Shamsul Akanda*



ABSTRACT

Two experiments, one irrigated and the other under rain-fed conditions were conducted simultaneously at the PNG University of Technology farm during 2004 and 2005 cropping season to determine the effect of late water stress on the tuber yield of 19 sweet potato genotypes and their genotypic variations based on physiological and morphological characteristics to drought response. Irrigated trial was sprinkler irrigated every alternate day except during the rainy days from planting to maturity, while the rain-fed trial only received natural rain. Large genotypic variations towards phonotypical characteristics were observed in both the situations. Severe stress at 74 to 96 days after planting in the rain-fed trial delayed the phenological development of late maturing genotypes, however, no significant effect on the early maturing genotypes as assimilate translocation to tubers occurred before severe stress developed. The late maturing genotypes tended to avoid stress by delaying its sinking and translocation of assimilates to tubers. The mean marketable tuber weight of different phenology and maturity groups did not differ significantly in the irrigated trial, but tuber yield was 8% lower in the late than in the early maturing groups under the rain-fed condition. Some genotypes under irrigated trial that performed poorly produced higher tuber weight under rain-fed condition. Mean total tuber weight for all the genotypes under rain-fed condition was reduced by 5.9% to 69% compared to the irrigated condition at various harvests. Total dry matter under rain-fed condition had a significant positive correlation with tuber number (0.62**) and marketable tuber weight (0.79**), but a negative insignificant correlation to drought score (-0.39). Marketable tuber weight had significant positive correlations with tuber number both under irrigated (0.80**) and rain-fed (0.67**) conditions.

Key words: sweet potato, genotypic variation, phenology, water stress, marketable tuber, drought score

INTRODUCTION

Water plays an important role for plant growth and development, since all plant physiological responses involve water. Sweet potato plant was found to be highly sensitive to water stress of 1-3 months duration when grown under sandy loam soils (Anselmo et al., 1998). During plant growth, changes in the amount of soil water due to prolonged drought can cause series of physiological interactions. Large genetic diversity in sweet potato currently grown in Papua New Guinea (PNG) and its wider adaptation from lowlands to highlands enables large variations in the agronomic and physiological responses (Kessavan and Tumana, 1986). There is also large variation in adaptation of sweet potato to wide ranges of moisture conditions. Some genotypes are suitably adapted to dry lowland environment, while others are better adapted to lowland wet humid conditions of PNG. Water stress of varying durations at different stages of plant development would be expected to interact with the tuber yield of sweet potato genotypes of different adaptation. Ludlow and Muchow (1990) reported tip dying of young leaves under water stress as a result of mechanical damage to cells after a decrease in cell volume due to dehydration.

____________________________________________________________________________________________ *Corresponding author: Tel: (675)-4734451, FAX: (675)-4734477, Email: [email protected] Article received on the 1st September, 2010; Accepted after revision on the 18th November, 2010


However, leaf senescence may be delayed physiologically when osmotic adjustment maintains the cell turgor to a lower leaf water potential (Ahamad et al., 1986). Variation in the rates of leaf development in young plants, stomata sensitivity to water deficit and leaf senescence may result in differing rates of water use. Genotypes which use water slowly may be able to avoid or limit the duration of severe water deficit. This would be important where drought occurs during vegetative stage, suberization and tuber bulking stage, a stage particularly sensitive to water deficit. When plants are water stressed during the later part of crop growth, dehydration tolerance would maintain metabolism in the plant and this may be important for tuber bulking from both current assimilate and translocated stored assimilate. Due to genotypic variation in translocation of stored assimilate, in some genotypes late water stress may not be detrimental to yield, if there are ample stored assimilates (Saraswati et al., 2002). However, if stress is prolonged, stored assimilate may be low, and the effects of late stress may be severe. The effects of water stress may differ among genotypes, if genotypic variation in phenology results in water deficit occurring at different phenological stages. Sweet potato in PNG is grown under rain-fed condition; however, drought is quite common during the growing season. To find the most adaptable sweet potato genotypes under water stress, two experiments were conducted with the objectives of determining the effect of late water stress on tuber yield of 19 sweet potato genotypes and to establish the physiological and the morphological basis for genotypic variation in drought response.

MATERIALS AND METHODS Site Description and Climatic Conditions The experiments were conducted at the PNG University of Technology farm, Lae, during 2004 and 2005 cropping season. The farm is situated in the north central coast of PNG mainland at an elevation of 65 meter above the sea level and between latitude of 6o 41� South and a longitude of 146o 98� East. The site is classified as lowland per humid climate (McAlpine et al., 1983) with an annual rainfall of 4,700 mm and mean monthly rainfall of 141mm. Minimum and maximum temperatures of 230 C and 300 C, while mean relative humidity of 86% at 0900 hrs 73% at 1500 hrs.

Experimental Design and Planting of Clones Two experiments were conducted in a randomized complete block design (RCBD) with 19 sweet potato genotypes chosen from the Sweet Potato Germplasm Collection of PNG University of Technology farm and replicated four times. A total land area of 1,035 m2 (45m x 23 m) was divided into four blocks of 5 m x 45 m. Each block was further divided into 19 sub-plots of 3 m x 5 m. The layout of both the trials was the same involving two adjacent trials, one under irrigation and the other under rain-fed condition. Each clone was planted on constructed ridges of 0.3 m height. In each plot, 60 cuttings of 30 cm apical portion of each 19 selected clones were planted at 30 cm x 100 cm.

Irrigated Trial This trial was sprinkler irrigated every alternate day from the time of field planting to maturity except during the rainy days so that it does not suffer from water shortage.

Rain-fed Trial This trial was completely rain-fed from the time of planting to final harvest. No supplemental irrigation was done in the absence of rainfall. At 74 days after planting (DAP), severe water stress occurred due to low rainfall of 17, 74 and 68 mm during the month of October, November and December, respectively when the plants were at the bulking stage.

Niugini Agrisaiens 2, 17-25, 2010 Sweet potato yield under late water stress Wamala and Akanda

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Fertilizer Application and Crop Management Both trials were top dressed with 12:12:17 fertilizer at 70 kg/ ha at 30 DAP. Weeds were controlled manually every three weeks, while insect pests, such as hawk moth caterpillars were controlled by spraying �Karate� at 20 milliliters per 15 liters of water as and when necessary. Data Collection The effects of water stress on leaf area were determined by measuring the LA for all the 19 genotypes at 43, 74, 95 and 125 DAP using the Leaf Area Meter (Model: LI-3000A). Fifty fully opened leaves were randomly collected from six sampled plants for each variety to measure the LA. Tuber dry matter (TDM) for the 19 sweet potato genotypes were measured at each harvest. For each genotype, a random subsample of 500 g fresh tuber was cut, weighed and dried in the hot air oven drier for five days and dry weights taken to determine the dry matter. At each harvest, tuberous root formed were counted and weighed to obtain the total tuber weight (g) for each genotype. Marketable tuber numbers and weights were taken by separating the marketable tubers from non-marketable tubers and weighed. Marketable tubers are those which weigh more than 750 grams and can be sold at market for consumption. Tuber - biomass partition for each clone was determined using the formula: Total tuber weight Tuber - Biomass Ratio = ------------------------------ Total tuber weight + Total top weight Tuber - biomass ratio under stressed condition is important to determine the cultivars with high tuber yield but less vine weight. The effects of adequate water and water stress in plants were shown by morphological characteristic symptoms of leaf drying and leaf senescence. For both trials, drought symptoms of leaf senescence and drying were scored visually using the Standard Evaluation System (IRRI, 1975) similar to drought screening for rice before and during the stress period. Each genotype was given the average score on a 1-5 scale; 1 being no symptoms of water stress with leaves still green and 5 showing all the leaves with dead tips longer than 8 cm and plants were dead (Turner et al., 1986).

Statistical Analysis

All the data collected from the two experiments were statistically analyzed using the Statistix software. Analysis of variance (ANOVA) was carried out for total fresh tuber yield, total dry matter, tuber dry matter, tuber - biomass ratio, leaf area and drought score. Least significant differences (LSD) and Duncan Multiple Range Test (DMRT) were used for mean separation of the selected parameters as applicable. Correlation between characters was also run to compare if various growth parameters were strongly dependent on each other.

RESULTS Phenotypic Variability The 19 genotypes used in this study varied widely in terms of phenotypic characteristics. All the genotypes were of twining type; however, leaf color was either green or purple. Tuber skin and flesh colour ranged from white to purple, red and orange. The vine length ranged from 200 to 500 cm and the leaf area from 24 to 53 cm2.

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Table 1. Total tuber weight (g) of nineteen genotypes at 43, 74, 95 and 125 days after planting in the rain-fed and irrigated trial

Genotypes

43 DAP 74 DAP 95 DAP 125 DAP

Irrigated Rain-fed

Irrigated Rain-fed Irrigated Rain-fed Irrigated Rain-fed

B-11 135.77 35.25 559.30 458.75 2739.3 2689.30 3418.80 3053.80

DOY-2 175.47 40.00 554.40 503.75 1763.0 161300 2418.80 2218.80

K9 125.38 24.75 418.43 293.00 1260.5 1235.50 2252.50 2177.50

KAV-79 119.35 25.50 315.55 164.00 1032.3 757.30 1218.80 1043.90

L329 133.10 32.50 548.02 442.50 1850.5 1050.50 2871.30 2746.30

L43 146.85 46.25 657.50 578.75 2453.3 2453.30 2867.50 2342.50

L676 126.92 26.25 486.73 352.50 1767.8 1567.80 2662.50 2562.50

L996 134.45 34.00 456.77 331.25 2144.5 1394.50 2235.00 2185.00

Mas-1 140.88 88.00 398.52 248.00 864.80 617.30 1717.50 1717.00

NUG2 118.03 17.50 371.38 190.75 858.00 933.00 1872.50 1772.50

NUG5 128.63 28.00 369.42 215.00 1170.30 1145.30 1540.00 1465.00

POI-13 134.38 44.00 435.68 410.00 2627.30 2427.30 3331.50 3024.00

RAB32 136.55 111.00 516.65 414.00 1331.50 1831.50 2466.30 2296.30

RAB36 136.97 36.50 529.55 404.00 2112.00 2211.00 3068.80 2768.80

RAB44 143.55 43.00 625.40 448.75 2252.50 2132.50 2587.50 2173.50

SI-172 130.67 30.00 614.30 513.75 2592.00 204200 3926.30 3645.00

SI-2 139.13 38.50 582.83 456.25 2690.00 2390.50 3656.30 3506.00

SIWAE 113.67 27.00 475.70 400.00 1539.00 1184.00 2193.80 2042.30

TIS-2478 132.95 47.50 406.83 356.25 1097.80 842.80 1528.00 1403.00

Mean 134.35 40.81* 490.68 377. 96** 1776.1 1670.5**

2548.3

2323.3**

*, **, the means under the rain-fed conditions are significantly different at p ≤ 0.05 and p ≤ 0.01(LSD), respectively from the corresponding means under the irrigated condition.

Total Tuber Weight At 43 DAP, total tuber weight per plot varied greatly between genotypes both in the rain-fed and irrigated trial (Table 1). Total tuber weight ranged from the lowest of 113.67g in SIWAE to the highest of 175.47g in DOY2 in the irrigated trial. However, total tuber weight in the rain-fed trial was far less than the irrigated trial with NUG2 showing the lowest of 17.5g and the highest in RAB32 with 111g. There were drastic tuber yield reductions in all the genotypes under rain-fed condition compared to the irrigated trial. Similar responses in total tuber weights were observed for 74 to 95 DAP in all the genotypes. From 95 - 125 DAP, late water stress was severe because of low rainfall during October to December and the tuber yield was reduced. The grand mean of total tuber weight for all the genotypes under rain-fed trial at 43, 74, 95 and 125 DAP was reduced by 69%, 22%, 5.9% and 8.8%, respectively from the corresponding grand means under the irrigated trial (Table 1). At 43 DAP, the tuber weight was drastically reduced compared to 95 and 125 DAP. Significant decrease in the total tuber weight was also observed in NUG5, MAS1 and NUG2 indicating the genotype susceptibility to water stress. The SI-172, SI-2, B 11, POI-13, RAB36, L329 and L43 had consistently higher yields from 74 to 125 DAP. Treatment mean comparisons for the total tuber weights in the irrigated and the rain-fed trials at 125 DAP are shown in Table 2. Significant variations in tuber weight response existed among the genotypes in both the trials.

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Table 2. Comparison of mean tuber weight at maturity (125 DAP) under irrigated and rain-fed conditions

a) Irrigated b) Rain-fed

Fig 1. Marketable tuber weight of 19 sweet potato genotypes under irrigated and rain-fed conditions

a) Irrigated

Genotype Tuber weight (g) Genotype Tuber weight (g)

SI-172 3926.3a SI-172 3645.0a

SI-2 3656.3ab SI-2 3506.3ab

B-11 3418.8abc B-11 3053.8abc

POI-13 3331.3abc POI-13 3024.0abcd

RAB36 3068.8abcd RAB36 2768.8bcde

L329 2871.3bcde L329 2746.3bcde

L43 2867.5bcde L43 2342.5cdef

L676 2662.5bcdef L676 2562.5cdef

RAB44 2587.5cdef RAB44 2137.5efgh

RAB32 2466.3cdefg RAB32 2296.3cdefg

DOY-2 2418.8cdefg DOY-2 2218.8cdefgh

K9 2252.5defg K9 2177.5defgh

L996 2235.0defgh L996 2185.0defgh

SIWAE 2193.8defgh SIWAE 2042.8efgh

NUG2 1872.5efgh NUG2 1772.5fghi

MAS-1 1717.5fgh MAS-1 1717.5ghhi

NUG5 1540.0gh NUG5 1465.0ghi

TIS-2478 1528.0gh TIS-2478 1403.0hi

b) Rain-fed

KAV-79 1218.8h KAV-79 1043.3i

Means followed by the same letter in a column are not significantly different at p ≤ 0.05 (DMRT)

21


Fig 2. Leaf area (cm2) increase in 19 sweet potato genotypes under irrigated and rain-fed conditions



Fig 3. Drought score for 19 sweet potato genotypes under irrigated and rain-fed conditions

22


The five top genotypes, SI-172, SI-2, B 11, POI-13, and RAB36 in terms of total tuber yield were same for both the trials. The total tuber yield differences among the five top genotypes was not significant at p ≤ 0.05 (DMRT). The five bottom ranking genotypes, NUG 2, MAS-1, NUG 5, TIS-2478 and KAV � 79 were also same for both the trials and the tuber yield differences among themselves were not significant at p ≤ 0.05 (DMRT).

Marketable Tuber Weight (g) Figure 1 shows the marketable tuber yield at 43, 74, 95 and 125 DAP for the irrigated and rain-fed trials. Marketable tuber weight was reduced by about 8% in genotypes NUG5, NUG2, SIWAE, MAS-1, DOY2 and RAB32 under rain-fed trial compared to the irrigated one. Under rain-fed condition, increase in marketable tuber weight was more evident for genotype SI-2, L996, L676, L329, and RAB36 at maturity (125 DAP) showing some degree of drought tolerance or resistance.

Leaf area (LA) Figure 2 illustrates the leaf area increase at 43, 74, 95 and 125 DAP for 19 genotypes both under irrigated and rain-fed conditions. Total leaf area increase was greater under irrigated condition than under the rain-fed condition with late stress. Leaf area increase under irrigated condition was much faster during the vegetative stage (43 � 95 DAP) than the maturity stages (95 � 125 DAP). However, under the rain-fed condition, LA increased rapidly at 74 � 95 DAP and then decreased drastically at 95 � 125 DAP because of drought at 74 � 95 DAP due to low rainfall.

Leaf Senescence and Drought Score The Figure 3 a, b shows the drought scores under irrigated and rain-fed conditions. It was observed that leaf senescence was most evident in some genotypes as the drought was prolonged towards maturity stage. At 95 DAP i.e. 15 days after occurrence of stress, the more sensitive and susceptible genotypes tend to show early senescence with highest maximum scores of 3.3, 3.0, and 2.8 in B11, DOY-2 and SI-172, respectively. Severe leaf drying continued for genotypes B11, K9, SI-2, SI-172 and TIS 2478, while slight leaf drying was observed for L676, L996, L43 and L329 as stress was prolonged. It was noted that most of the genotypes did not show leaf drying symptoms until after 95 DAP or 15 days after the occurrence of the water stress compared to the irrigated condition. Under rain-fed condition at 125 DAP, most leaf drying occurred in SI-2, B11, SI-172, MAS 1, SIWAE, TIS 2478 and RAB 44. In contrast, under the irrigated trial, leaf drying and senescence was lower than the rain-fed trial (Figure 3 a).

Table 3. Pearson�s correlation coefficients for the 19 sweet potato genotypes grown under irrigated and rain-fed conditions

Leaf area MTNUM MTWT DSC TDM

MTNUM 0.198 (0.396)

MTWT 0.267 (0.228)

0.671** (0.796**)

DSC 0.113 (-0.127)

-0.341 (0.243)

-0.455 (0.197)

TDM 0.365 (0.354)

0.623** (0.552**)

0.792** (0.624**)

-0.389 (0.203)

TTWT 0.182 (0.224)

0.719** (0.738**)

0.657** (0.726**)

-0.177 (-0.010)

-0.746** (0.630**)

Numbers with in the parentheses ( ) are the correlation coefficients under the irrigated condition *, **, correlation coefficients are significant at p ≤ 0.05 and p ≤ 0.01, respectively MTNUM = mean tuber number, MTWT = marketable tuber weight, DSC = drought score, TDM = total dry matter, TTWT = total tuber weight.

23


Interrelationship of Different Parameters Correlation coefficients among leaf area, marketable tuber weight, mean tuber number, total dry matter, total tuber weight and the drought score for the rain-fed and irrigated trials are presented in Table 3. Total dry matter was positively correlated to leaf area (r= 0.365), tuber number (r= 0.623**), and marketable tuber weight (r= 0.792**) but negatively to drought score (r= -0.389) under the rain-fed condition; however, it was positive (r= 0.203) for the irrigated trial. Only correlation among total dry matter, tuber number and marketable tuber weight were significant. Total tuber weight was positively correlated to leaf area (r= 0.182), tuber number (r= 0.719**), marketable tuber weight (r= 0.757**) and total dry weight (r= 0.746**) but negatively to drought score (r= -0.177) and it was same for both the trials. The correlation coefficients only for tuber number, marketable tuber yield and total dry matter were significant. Marketable tuber yield was positively correlated to both leaf area and the tuber number and it was significant only for tuber number in both the trials. Drought score was negatively correlated to tuber number and marketable tuber yield but positively to leaf area under the rain-fed condition, and none of these were significant. However, in case of irrigated condition, drought score was negatively correlated to leaf area and positively to tuber number and marketable tuber weight and none of these were significant. Again, leaf area was positively correlated to mean tuber number for both the trials but was not significant.

DISCUSSION Superior adaptability of a crop genotype against biotic and abiotic stresses along with improve yield and quality are essential for wider acceptability. Genetic, agronomic and physiological characteristics play a vital rolein this regard. Large phenotypic variations on the measured characters for the phenological development were observed among the 19 genotypes used in this experiment. In the rain-fed trial, severe stress at 74 DAP delayed the phenological development of late maturing genotypes, NUG5, NUG2, SIWAE, MAS-1, and KAV79, while stress did not have substantial effect on the early maturing genotypes as translocation of assimilates to tubers occurred before the occurrence of severe stress. It was also noted that late maturing genotypes tended to avoid stress by delaying its sinking and translocation of assimilates to tubers which is in consistent with the findings of Saraswati et al. (2002). Water stress had more severe impact on the late maturing genotypes than the early maturing genotypes when tuber initiation occurred (after 75 DAP). It was observed that tuber bulking was deferred until the stress was relieved. This was in consistent with the observation of Sung (1985), Anselmo et al. (1998) and Taufatofua (1996) reported that severe stress during the vegetative phase delayed tuber initiation of sweet potato until after rainfall occurred. Stress during tuber development would have resulted in damage to tubers and a reduction in sink size. It is likely that the reduced sink size caused some early genotypes to increase canopy and vine weight after stress was relieved. The increase in vine weight and canopy formation extended duration of tuber development in the late maturing genotypes. Towards the end of stress period at final harvest (125 DAP), the highest marketable tuber yield was observed in genotypes L996, L43, RAB44, L329, SI-2 and L676, while lowest marketable tuber weight was with NUG5, NUG2, SIWAE, MAS-1, KAV79 and DOY 2. It was also observed that genotypes with less leaf area and deeply lobed leaves showed increase in marketable tuber weight. Genotypes with less leaf area that produced high marketable tuber yield could have been due to less water loss from the reduced leaf surface area as a result of leaf lobbing. Less water loss from the leaf surface in the above genotypes enabled turgor maintenance by mesophyll cells during the stress period (Saraswati et al., 2002). In the irrigated trial, marketable tuber yield was related to the dry matter increase during the bulking stage. The mean marketable tuber weight of different phenology and maturity groups did not differ substantially in the irrigated trial, but tuber yield was reduced by 8% in the late than in the early maturing groups in the rain-fed trial. It was noted that the genotypes that performed poorly under irrigated condition produced high tuber weight under rain-fed condition. The differences between marketable tuber yield and total dry matter increase during bulking is assumed to be translocation from post-vegetative assimilates in the leaves (Lowe and Wilson, 1975).

24


Marketable tuber yield in the five genotypes was significantly lower than the post vegetative dry matter increase, suggesting that these genotypes were sink limited. (Ludlow and Muchow, 1990). Total tuber weight was greatly reduced at early vegetative stages of growth (43 DAP) in the rain-fed trial compared to the irrigated one. This tuber weight reduction at 43 DAP under stress was attributed to plants not fully developed in terms of root development. However, as plants increased putting on more roots and canopy, total tuber weight began to increase. It appears that plant growth in the irrigated trial for genotypes, NUG 5, NUG 2, SIWAE, MAS-1, and KAV- 79 was also limited by excessive moisture and other factors as tuber yield, TDM were lower than in the rain-fed trial. This is in consistent with the findings of Alves and Setter (2004). Of the five late maturing genotypes, NUG 5, NUG 2, SIWAE, MAS-1, and KAV 79, TDM harvested at 74 DAP in rain-fed trial was 30.9 to 86.1% of the TDM at 74 DAP in the adjacent irrigated trial. Water stress greatly reduced the TDM of late maturing genotypes compared to the irrigated trial. Plants in irrigated trial matured earlier than those under the water stress due to conditions that may have been more conducive to water stress during tuber bulking in the irrigated trial than in rain-fed trial (Indira and Kabeerathuma, 1988).

Conclusion Genotypic variations in tuber yield were found in both water regimes. Plant growth rate ceased during the late water stress period for all the genotypes. There was, however, genotypic variation in plant water status and this appeared to be related to radiation load. Drought score was positively correlated to leaf area, but negatively to dry matter production and total tuber weight. There was variation in recovering ability that affected tuber yield, particularly for early maturing genotypes, where stress period was short.

REFERENCES Ahamad, S., Kobata, T. and Takami, S. (1986). Role of avoidance and tolerance to water deficits in seedling survival of

diverse rice (oryza sativa). Japanese Journal of Crop Science 55: 327-332. Alves, A. C. A. and Setter, T. L. (2004). Response of cassava leaf area expansion to water deficit. Annals of Botany 94

(4): 605-613. Anselmo B. A., Ganga, Z. B., Heimer, E. O. and Nejidat, Y. M. (1998). Screening sweet potato for drought tolerance.

Tropical Agriculture (Trinidad) 75 (2): 189�196. Indira, P. and Kabeerathuma, S. (1988). Physiological response of sweet potato under water stress, 1. Effect of water

stress durin the different phases of tuberization. Journal of Root Crops 14(2): 37-40. IRRI (International Rice Research Institute) (1975). Standard evaluation systems for rice. Los Banos, Philippines. pp 64. Kessavan, K. and Tumana, C. (1986). The evaluation of poly-cross hybrids of sweet potato. Science in Niugini. pp. 76-

79. Ludlow, M. M. and Muchow, R. C. (1990). Critical evaluation of traits for improving crop yields under water limited

environments. Advances in Agronomy 43:107�153. Lowe, S. B. and Wilson, L. A. (1975). Yield and yield components of six sweet potato cultivars. II. Variability and

possible sources of variation. Experimental Agriculture 11:49-58. McAlpine, J. R., Keig, G. and Falls, R. (1983). Climates of Papua New Guinea, CSIRO; Australian Natl Univ. Press. pp

5-46. Saraswati, P., Johnston, M., Coventry, R. and Holtum, J. (2002). Identification of drought tolerant sweet potato (Ipomoea

batatas (L.) Lam) cultivars. http: www.crop science.org.au / In: Proc. of Inter. Crop Sci. Conf. 2004. Sung, J. M. (1985). Studies on physiological response to water stress in sweet potato. II. Osmotic adjustment in sweet

potato. Sweet Potato Journal of Agricultural Association of China 129: 50-55. Taufatofua, P. (1994). Agronomic manipulation of sweet potato grown under water limiting conditions. PhD Thesis,

The University of Queensland. pp 14- 86. Turner, N. C., O�toole, J. C., Cruz, R. T., Namuco, O. S. and Ahamad, S. (1986). Response of seven diverse rice cultivars to water deficit. I. Stress development canopy temperature, leaf rolling and growth. Field Crop

Research 13:257-271.

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http://www.crop

Volume 2, 26� 29, 2010

Niugini Agrisaiens Research Article A STUDY ON SCREENING FOR RESISTANCE TO VASCULAR STREAK

DIEBACK IN COCOA

James Butubu, Shamsul Akanda* and Tom Okpul



ABSTRACT

Two in vitro studies were conducted to evaluate the growth of Oncobasidium theobromae, the causal organism for vascular streak dieback of cocoa on 2% water agar, nutrient agar and V-8 juice agar and to investigate the efficacy of artificial leaf disc screening method. The fungus grew very well on nutrient agar and V-8 juice agar but the growth on water agar was very poor and inconsistent. The fungus did not produce any spore on any of the media. The leaf disc inoculation method using mycelia was able to discriminate the known resistant and susceptible genotypes. Fungal colony growth on K82, the susceptible genotype was significantly higher (p ≤ 0.01) than the clones 38-10/3 and 73-2/2 having moderate and resistant field reactions, respectively. The growth rate difference between 38-10/3 and 73-2/2 was non-significant. The leaf disc screening method needs to be refined further involving tests with large numbers of susceptible and resistant genotypes to determine the correlation between the laboratory and field reactions before it could be routinely used for in vitro screening of genotypes at the seedling stage.

Key words: cocoa, vascular streak dieback, resistance, in vitro, leaf disc

INTRODUCTION

Cocoa (Theobroma cacao L.) is one of the most important export crops of Papua New Guinea (PNG). PNG produces about 42,000 to 46, 000 tonnes of cocoa beans annually (FAO, 2003) and more than two thirds of that is produced by the smallholders contributing significantly to the country�s economy in terms of employment and improvement in the life style. Production of cocoa is affected by several diseases. Two most important fungal diseases that cause substantial yield losses in PNG are phytophthora pod rot (Ppr) caused by Phytophthora palmi-

vora and vascular streak dieback (VSD) caused by Oncobasidium theobromae. The VSD first reached its epi-demic in 1960s destroying many plantations (Keane et al., 1972). The yield losses due to VSD were estimated to range from 25 to 50% or sometimes as high as 100% in very susceptible cultivars (Dennis, 1991; Keane, 1992). Similar yield losses have also been reported in Malaysia (Bong and Seow, 1989). Efforts to re-establishment and infill affected plantations proved to be very difficult both in PNG and Malaysia. This is because young seedlings are more susceptible (Lam et al., 1988; Guest and Keane, 2007) and the casualty rate could be 80% or more (Bong, 1982). The use of resistant cultivars is the most important option to tackle the disease because it is cost effective, environmentally friendly and compatible to other management practices. The success of any effective and efficient disease resistance breeding program depends partly on efficient screening methods, understanding of the genetic makeup of the parental lines and the inheritance pattern of the concerned disease (s). The genetic study on the resistance of cocoa to VSD and Ppr is an important part of cocoa breeding in Cocoa Coconut Institute in PNG (CCIPNG). The success of this program also depends on the avail-ability of a simple, cost effective and reliable methodology for screening large number of seedlings for resistance to P. palimovora and O. theobromae. In PNG, VSD is normally screened through �disease plot� methods under

____________________________________________________________________________________________ *Corresponding author: Tel: (675)-4734451, FAX: (675)-4734477, Email: [email protected] Article received on 30th August, 2010; Accepted after revision on 20th October, 2010


natural condition (Efron et al., 2002) as there is no reliable artificial inoculation technique, because O. theobromae does not sporulate routinely in axenic culture (Varghese et al., 1981; Musa, 1983). This is a major drawback in artificial screening of large number of genotypes and is responsible for slow progress in resistance breeding for VSD. Therefore, two laboratory studies were conducted to: i) isolate and culture O. theobromae in different artificial culture media; and ii) investigate the efficacy of in vitro leaf disc inoculation method for screening against VSD.

MATERIALS AND METHODS Two different studies were conducted at the Unitech Biotechnology Centre (UBC) of the PNG University of Technology in 2006. In the first experiment, O. theobromae was isolated and grown in three different culture media, namely 2% water agar, nutrient agar (NA) and V-8 juice agar. Infected stem pieces were collected from the field nursery in Murunas, CCIPNG, Madang. Small pieces of 5 cm length were surface sterilized with 1.5% sodium hypochlorite solution, rinsed twice in distilled water and placed on 2% water agar. The fungus was allowed to grow and was purified through hyphal tip culture. The purified fungus was then grown on NA medium. A 3 mm diameter agar disc was cut and used to inoculate the plates with 2% water agar, NA and V-8 juice agar media by placing the disc at the centre of the plates. The plates were incubated at room temperature of about 300C, organized in a randomized complete block design and replicated four times. Colony diameters were recorded each day until day 7 when the petri-dishes fully covered. The second experiment was also conducted at the UBC to investigate the efficacy of leaf disc inoculation technique to screen cocoa against VSD. Leaves of locally available susceptible genotype K82 and resistant genotypes 38- 10/3 and 73-2/2 were used in this study. The second and/or third fully developed leaves from the growing tip were collected for preparing the leaf discs for inoculation. Leaf discs of 18mm in diameter were cut out using an 18 mm cork borer from each of the cultivars and surfaced sterilized with 1.5% sodium hypochlorite and rinsed twice with distilled water. One disc each from test cultivars was placed in each petri-dish with a thin film of water and inoculated with the 4 mm disc of the fungus grown for five days on NA medium. The experiment was set in a randomized complete block design with each of the treatment (cultivars) along with a control (no inoculation) replicated four times. The plates were placed on the bench top at room temperature (approx. 300C) and the diameter of the fungal colony was measured daily for five days.

Data Analysis The data collected on both the trials were subjected to ANOVA and mean separation (LSD) using the statistical package STATISTIX.

RESULTS AND DISCUSSION

The mean colony diameter on NA, V-8 Juice agar and WA was 84.9, 85.5 and 7.0 mm respectively. The mean colony diameter on water agar was significantly lower (p ≤ 0.05, LSD) than the growth on NA and V-8 juice agar. The mean colony diameter on V-8 juice agar was slightly higher than on NA, but it was non-significant. The fungal growth on WA was very slow and mycelium production was sparse compared to NA and V-8 juice agar. WA (nutrient poor medium) was used to stimulate spore production (Prior, 1980) in O. theobromae. However, fungal growth was observed to be very slow and inconsistent upon subsequent sub-culturing (Keane and Prior, 1991). The good growth on V8 juice agar and NA was expected as they have the adequate nutrients to support the growth of the fungus. The fungus did not produce spore in any of the culture media. This could be due non-suitability of the culture media and lack of essential growth conditions, like temperature and aeration (Lam et al., 1988). Dennis and Holderness (1992) also in a laboratory test with field collected basidiomes revealed that sporulation require alternating light and dark cycle, temperature of 25±20C and relative humidity of above 95%.

Niugini Agrisaiens 2, 26-29, 2010 In vitro screening for VSD Butubu et al.

27

The fungal growth diameter on leaf discs showed highly significant (p ≤ 0.01) differences among the cultivars. The mean growth diameters were 10.5, 9.2 and 8.2mm respectively for K82, 38-10/3 and 73-2/2. The colony diameter on K82 was significantly higher than 38-10/3 and 73-2/2, however, there was no significant growth difference between 38-10/3 and 73-2/2. The higher susceptibility of K82 is also in line with the findings of Efron et al. (2002) from a field experiment. Oncobasidium theobromae is an endogenous (vascular tissue inhibiting) pathogen (Dennis and Holderness, 1992). Under favourable conditions, it may grow on fresh tissues as in this case fresh leaf discs. However, on leaf discs, growth decline with time may be due to the deterioration of the leaf constituents, such as extracellular enzymes, hormones, polysaccharides, etc. Water is also an important component which may have affected the growth of the fungi. With time leaf discs were dehydrated, thus inhibiting the growth that may lead to the death of the advancing mycelium. This behavior strongly supports the non-saprophytic nature of the O. theobromae. Similar chlorotic reaction observed on un-inoculated and the inoculated leaf discs may be due to natural senescence and not due to cellular death from fungal infection and colonization.

Conclusion Oncobasidium theobromae did not sporulate on WA, V-8 juice agar and NA at room temperature of 300C, but grew well on the latter two media. The preliminary test showed that leaf disc artificial screening method can discriminate the genotypes based on their level of resistance. This may provide useful information for the development of an artificial leaf disc screening method for VSD resistance. Further work is necessary to standardize the protocol with large numbers of genotypes including the proper susceptible and resistant checks. The results also need to be compared with the established field protocol, �disease plot� to determine any correlation.

ACKNOWLEDGEMENTS This research was supported by a Scholarship grant ASEM/2004/077 from the Australian Centre for International Agricultural Research (ACIAR).

REFERENCES Bong, C. L. (1982). Some important diseases of cocoa in Sabah. Seminar Koko Untuk Pembangunan

Pertanian Negara, Cocoa Research Station, Quion Hill Tawau, Sabah, Malaysia. Bong, C. L. and Seow, S. T. (1989). Chemical control of VSD on mature cocoa. Technical Bulletin No. 9:23- 42. Department of Agriculture, Kota Kinabalu, Sabah, Malaysia. Dennis, J. J. C. and Holderness, M. (1992). Weather patterns associated with sporulation of Oncobasidium

theobromae on cocoa. Mycological Research 96 (1): 31-37. Efron, Y., Faure, M., Saul, J. and Blaha, G. (1999). Disease resistance studies and breeding in Papua New Guinea. In: Proceedings of the International workshop on the contribution of the disease resistance to cocoa variety improvement. 24-26 November, 1999. Salvador Bahai, Brazil, INGENIC, 181-182 pp. Efron, Y., Marfu, J., Faure, M. and Epaina, P. (2002). Screening of segregating cocoa genotypes for resistance to vascular streak dieback (VSD) under natural conditions in Papua New Guinea. Australian Plant Pathology 31: 315-319. FAO (2003). Summary of world food agricultural statistics. Publishing management services, Information

Division. FAO, Rome: Italy.

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28

Guest, D. and Keane, P. (2007). Vascular Streak Dieback: A new encounter disease of cocoa in Papua New Guinea and South Asia caused by the obligate Basidiomycete Oncobasidium theobromae.

Phytopathology 97:1654-1657. Keane, P. J. and Prior, C. (1991). Vascular Streak Dieback of cocoa. Phytopathological Papers 33: CAB International, Mycological Institute. Keane, P. J., Flentje, N. M. T. and Lamb, K. P. (1972). Investigation of vascular streak dieback of cocoa in Papua

New Guinea. Australian Journal of Biological Sciences 25:553-564. Lam, C. H., Varghese, G. and Zainal Abidin M. A. (1988). In vitro production of Oncobasidium theobromae

basidiospores. Transactions of British Mycological Society 90(3): 505-507. Musa, M. J. (1983). Coconut water as culture medium for Oncobasidium theobromae. Malay Agricultural

Research and Development Institute Bulletin 11:107-110. Prior, C. (1980). Vascular streak dieback. Cocoa Growers� Bulletin 29:21-26. Varghese, G., Zainae bidin M. A. and Mainstone, B. J. (1981). Vascular streak dieback of cocoa in Malaysia. II.

Isolation and culture techniques of causal pathogen. The Planter 57:576-580.

Niugini Agrisaiens 2, 26-29, 2010 In vitro screening for VSD James et al.

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Volume 2, 30� 38, 2010

POTENTIAL OF NEWLY BRED SWEETPOTATO CLONES AS IMPROVED CULTIVARS UNDER HIGHLAND CONDITIONS OF

PAPUA NEW GUINEA I. Performance of Early Maturing Sweetpotato Clones

R. K. Kapila*, B. Wera, M. Deros, R. P. Pawilnga, S. Ivahupa1, G. Bagle2, T. Okpul3,

and E. Guaf2 NARI Highlands Regional Centre, P.O Box 384

Aiyura, Eastern Highlands province, Papua New Guinea

ABSTRACT

Sweetpotato (Ipomoea batatas L.), the most important staple crop of Papua New Guinea (PNG) has important place on agricultural Research and Development (R&D) agenda of the nation. Sweetpotato breeding programme aimed at developing early maturity high yielding clones with resistance to prevalent diseases and acceptable culinary traits, generated more than six hundred genetically recombinant seeds through polycross mating among twelve selected parents. Scarified seeds were germinated and 72 plants established from the seedlings exhibited storage root formation potential. Selection intensities ranging from 12-88 per cent with an overall selection pressure of 0.48 per cent were employed at different stages where 6 elite clones were identified viz., 5ML 7e, 5ML 11g, AL 7h, AL 9l, BL 3b, and BL 6i. Their evaluations in replicated trials at NARI Highlands Regional Centre, Aiyura revealed yield superiority over local popular cultivars, Waghi Besta and Wanmun. Overall mean storage root yield from two trials during dry and wet seasons ranged from 9.26 to 15.89 t ha-1 following low-input farming practices. Clones BL 3b and BL 6i exhibited better resistance to sweetpotato scab (Elsinoe batatas) under field conditions as compared to better local check, Waghi Besta. Taste evaluations indicated high consumer acceptability for 2 recombinant clones, BL 6i and AL 9l, at par with locally preferred cultivar, Waghi Besta. Clone 5ML 7e also exhibited yield stability under adverse conditions, particularly under dry conditions. Based on evaluations for all traits, clone BL 6i was identified as most promising recombinant clone, closely followed by BL 3b and 5 ML 7e. These clones are undergoing further evaluation under advanced trials at present to further validate their potential before their release as first locally bred early maturing commercial cultivars of PNG. Key words: Breeding, Ipomoea batatas (L.), polycross mating, early maturity, leaf scab

_________________________________________________________________________________________ *Corresponding author: Tel: +675 537 3500, FAX: +675 537 3516, Email: [email protected] 1Present address: Australian National University Enterprise, PNG LNG Project, Southern Highlands, Papua New Guinea; 2 NARI Momase Regional Centre, PO Box 1639, Lae 411, Morobe Province, Papua New Guinea; 3UNITECH Biotechnology Centre, Agriculture Department, PNG University of Technology, Lae, Morobe Province, Papua New Guinea.

Article received on 10th September, 2010; Accepted after revision on 19th November, 2010

INTRODUCTION

Sweetpotato (Ipomoea batatas L.) is the most important staple crop of Papua New Guinea (PNG) producing 66 % of food energy of the nation. Its annual production is estimated at 2.9 million tonnes per annum worth an estimated value of US$ 700 millions (Bourke and Vlassak, 2004). The crop has evolved from a mere pre-colonial introduction in Papua New Guinea highlands to a single major staple food energy source in about 300 years time (Watson, 1965). During this, the crop has not only ensured food security to the small and marginal farm holders of the nation, but has also elevated its importance from an introduction to a strategically important crop for the PNG. However, monoculture of crop and heavy dependence of the nation on it as staple food has made food security of the nation vulnerable due to potential biotic and abiotic threats in the long run.


Therefore, the situation warrants regular monitoring of crop�s production systems, threats etc. through a planned and continuous agro-technological interventions at the country level.

Although sweetpotato is the most important staple food crop of PNG, its productivity is far low in

comparison to average yields elsewhere. This low productivity is attributed to factors such as low yielding cultivars, susceptibility to pests and diseases, poor soil fertility and poor agro-technological interventions by farmers due to its subsistence crop status. Further, although sweet potato is bestowed with large potential genetic resources, molecular studies have reported its genetic base to be very narrow (Fajardo et al., 2002). This makes it imperative to broaden its genetic base by including appropriate diverse cultivars in the breeding program as a safeguard against potential future threats.

Multifaceted problems of sweetpotato delivery system can be tackled through integrated R&D approach

in PNG with a core of genetic improvement programme primarily aimed at achieving diversification of its genetic base. In addition to improving food security in PNG through broadening of its genetic base, there is considerable scope of enhancing the yield potential of the crop and its storage root quality for physico-chemical components including â-carotene, apart from improved tolerance to identified biotic and abiotic stresses, using appropriate breeding techniques. Early maturity is another primary breeding objective as it is helpful in commercial cultivation of the crop and can also be used as post drought management strategy for early regeneration for food security. Sustainable breeding programme shall not only ensure the food security but will also help achieving higher productivity and efficiency thus releasing land and other resources which can be diverted to achieve meaningful diversification of agricultural production systems in PNG. Continuous flow of improved cultivars, apart from making available high yielding genotypes, will also ensure supply of the quality pathogen free planting material to counter the negative impacts of pests and diseases towards achieving higher productivity.

The present research was thus directed towards achieving higher productivity in this crop through

development and release of improved sweet potato clones having higher yield potential, earliness to maturity, high carotene contents, taste acceptability and resistance to prevalent diseases through a breeding program started in 2005. The results of the present study on 2 gene pools, viz. early maturing and carotene rich clones are being presented in a series of 2 parts. The first part focuses on performance of early maturing and high yielding selections, while part II presents results of the evaluation of carotene rich OFSP clones with better consumer acceptability.

MATERIALS AND METHODS

Twelve elite clones of sweetpotato selected from germplasm based on their desirable traits including high storage root yield, early maturity, tolerance to drought, flesh colour (orange), flowering ability and other desirable horticultural traits as potential parents, were planted in a polycross mating design at farmer�s fields around Kainantu area in Eastern Highland Province under a farmers� participatory breeding program (Table 1). Random cross pollination among parents was promoted by staking them on inverted �V� shaped structures to expose flowers of all parents equally to visiting pollinators. Genetically recombinant true half-sib seeds set on each parental clone were collected after flowering season.

The collected seeds were scarified manually using scalpels to break hard seed coat and soaked in water for 48 hours to induce germination before transfer to the nursery bed. Properly filled heavy mature seeds were separated from unfilled immature floaters by immersing the seeds in beakers containing water before sowing in nursery bed containing a sterilized medium of three parts top soil, two parts sand and one part of chicken manure. The seeds were sown at 4 and 5 cm plant to plant and row to row spacing, respectively. Observations on the germination were recorded 2-3 weeks after sowing. Seedlings exhibiting storage root formation potential in the nursery were advanced for further observations on single hills in the field.

Niugini Agrisaiens 2, 30-38, 2010 Potential of early maturing sweetpotato clones Kapila et al.

31

Field screening and evaluation of the selected new clones to date include single cycle of hill and preliminary trial, and two replicated Initial Evaluation Trials (IETs) in 2 separate growing seasons. Further evaluation of these clones in two Advanced Evaluation Trials (AETs) is under progress. The selected clones were planted on single hills at a spacing of 1m (row to row and plant to plant). Observations and selection from planting to harvest were made on growth habit, and pest and disease incidences, early storage root formation, better yield potential, good storage root shape and colour, storage root number, storage root skin texture and defects. Clones exhibiting the above characteristics were selected with active participation from farmers. The selected early maturing high yielding clones were advanced for evaluation under Preliminary Trial. Five plants of each clone planted in a row were subjected to sequential harvesting to assess earliness of the clones. Single plant from each clone was harvested at fortnightly intervals starting 3 months after planting and concluding at 5 months. Clones exhibiting early storage root formation and other aforementioned desirable traits were advanced for evaluation under replicated IETs.

All activities involved in the screening and selection of new polycross clones were based at NARI

Highlands Research Centre�s Farm at Aiyura located 145.90° E and 06.35° S at an altitude 1660 m above sea level, except for the nursery selection. Selected clones in the initial trials were planted in a Randomised Complete Block Design with four replicates (RCBD) at a spacing of 1m between plants and rows with a net plot size of 4m2. The IET Cycle I & II comprised six newly bred clones as treatment along with 2 local cultivars, Waghi Besta and Wanmun as standard check to compare their performance with existing commercial varieties. No chemical fertilizers and pesticides were used in these trials. Other optimum conditions of management were maintained throughout the cropping period with manual weeding done twice during the crop growing season. IET Cycle I trial was planted in December, 2008 and harvested in April 2009, whereas IET Cycle II was planted in May, 2009 and harvested in October, 2009.

Table 1. Promising parent clones involved in a polycross

mating block under farmers� participatory breeding

program and their prominent desirable traits

1Drought tolerant; 2Early maturing; 3Orange Flesh

Sweetpotato; 4Pacific Regional Agricultural Programme; 5Highlands Sweetpotato Germplasm; 6Local Cultivars

No. Cultivar/Clone Type Source

1 PRAP 469 1DT/2EM 4PRAP

2 SSYK 026 DT/EM 5HSPG

3 WHCK 005 DT/EM HSPG

4 PRAP 559 DT/EM PRAP




8 SKK 010 DT/EM PRAP

9 WBS 010 DT/EM PRAP

10 Top 20/Kerot Hagen 3OFSP 6Local

11 2 Kina anta DT/EM Local

12 Maraso DT/EM Local


32

Leaf and stem scab (Elsinoe batatas [Saw.] Viegas and Jenkins) is a prominent disease affecting sweet potato mostly in the colder highlands of PNG. Scab assessment was done fortnightly throughout the cropping season after planting based on visual observation of the selected plants. For each sample plant, damage was scored and recorded on a scale from 1-5 as a reflection of per cent of leaf and/ stem area affected by scab. The scale is described as 1- highly resistant (0 % damage), 2 � resistant (1-25% damage), 3 � moderately resistant (26-50% damage), 4 � susceptible (51-75% damage) and 5 � highly susceptible (>75% damage).

The trials were harvested after assessing the maturity of the check varieties. All underground parts/

storage roots were cleared from adhered soil or debris. The storage roots were separated in to marketable edible (>100g, i.e. 180-250mm length & 60-75mm diameter) and non-marketable undersized small/pencil storage roots with irregular shapes (<100g i.e. 130-180mm in length and 50-60mm diameter). The total number of storage roots and fresh weights of the above categories were recorded accordingly for each plot.

Organoleptic evaluation of sweet potato clones was done through a group of panelist. General

appearance, odour, softness, taste, chewiness, sweetness, mealiness, stickiness, fiber content and overall acceptability of cooked storage roots of each clone were assessed by 10 tasters. Storage roots of all clones were subjected to only one most common cooking method, roasted (dry mumu) and were sliced into 5 x 5 cm pieces when cooked. Without knowing their actual identity, the samples were respectively and randomly assembled on the table with temporary code numbers on them. Each panelist had a chance to taste at least all the samples coming from each clone and score according to his/her own judgment on a 1-4 scale, where 1= least preferred and 4= most preferred. The panelists� overall impressions were computed and analyzed. The data collected on yield and yield components, and disease severities were subjected to analysis of variance (ANOVA) using Statistical Analysis Procedures (Genstat Discovery software Version 3). Fisher�s protected least significant difference (LSD) test was used to detect differences between means of the clones. RESULTS From more than six hundred recombinant seeds, five hundred and sixty were raised in nursery based on their satisfactory seed development. All recombinant clones were subjected to intensive selection pressure afterwards, based on the breeding objectives. From observable storage root formation ability, 12.8 % of the total germinated seedlings in nursery were selected for single hill trial of which 31.9 % were advanced for evaluation under preliminary trial (Table 2). From preliminary trial, 6 (26.08 %) of the clones were selected for further yield evaluations under replicated trials. Overall, 0.48 per cent of the total recombinant progenies harvested at seed level from polycross block ultimately constituted test material for intensive evaluation under replicated trials.

Evaluation of selected recombinant early maturing clones under IETs revealed that mean marketable

and total storage root yield for all test clones and checks, except 5ML 7e and Wanmun were higher during IET Cycle I as compared to Cycle II (Table 3). Overall mean for total storage root yield during IET Cycle I ranged from 10.39 (Wanmun) to 17.12 (BL 6i) t ha-1, whereas, during Cycle II it ranged from 6.96 (AL 9l) to 16.43 (5ML 7e) t ha-1. Recombinant clones, BL 6i and BL 3b demonstrated higher yield potential by significantly out yielding both check varieties during Cycle I. However, during Cycle II evaluation, there was decline in the yield of most of the clones and performance was at par with check, Wanmun. During this season, only Clone 5ML 7e could surpass the check variety Waghi Besta. Overall differential performance of all test clones and check varieties was observed over the seasons. Similar trend was also observed for mean marketable storage root yield. Marketable storage root yield was higher during Cycle I as compared to Cycle II. Clones, AL 7h, BL 3b and BL 6i yielded more marketable storage roots than Wanmun, whereas, BL 3b and BL 6i also out yielded better check variety, Waghi Besta during this season. During IET Cycle II, the performance of most clones was at par with checks, except clone 5ML 7e which out yielded Waghi Besta. Amongst the test clones and checks,


33

Selection Criterion (a) Total progenies produced/ evaluated

Number of progenies selected/ advanced

Selection intensity (%)

Crossing Block (CB) Proper seed development

630 560 88.88

Seedling Nursery (SN) Storage root formation ability of seedlings

560 72 12.85

Hill Trial (HT) Early maturity, storage root shape, colour, number, yield and pest and diseases

72 23 31.94

Preliminary Trial (PT) Early maturity, storage root shape, colour, number, yield and pest and diseases

23 6 26.08

Initial Evaluation Trial (IET 1 & 2)

Yield potential, culinary traits and pest and diseases incidence

6 3 50.0

Overall selection % 630 3 0.47

Table 2. Total population of recombinant progenies and selection intensities employed at different stages of SP breeding programme aimed at early maturity and high yields


Sweetpotato clones Mean storage root number per plant

Mean storage root yield per hec-tare (tons)1

Mean marketable storage root yield per hectare (tons)1

IET Cycle I

IET Cycle II

Mean IET Cycle 1

IET Cycle 2

Mean

5ML 7e 7.06 12.10 16.43 14.27 10.07 14.62 12.34

5ML 11g 5.38 10.64 7.23 8.94 8.89 6.29 7.59

AL 7h 3.66 13.68 9.65 11.66 13.12 8.94 11.03

AL 9l 3.06 11.57 6.96 9.26 11.05 6.50 8.78

BL 3b 7.41 16.78 11.24 14.01 15.77 9.19 12.48

BL 6i 6.59 17.12 14.65 15.89 15.77 12.93 14.35

Waghi Besta (Check) 6.03 12.26 10.16 11.21 11.36 7.76 9.56

Wanmun (Check) 5.97 10.39 11.82 11.11 9.16 10.65 9.91

Grand mean 5.64 13.07 11.02 12.04 11.90 9.61 10.75

LSD at P≤ 0.05 1.195 3.494 5.547 3.484 5.390

CV (%) 11.6 7.2 12.3 5.1 12.8

P-value <.001 0.002 0.021 0.001 0.040

1Yield based on a plot area of 4m2

Table 3. Performance of selected early maturing recombinant clones for storage root yield and other component traits under IET Cycles I & II

34

mean storage root number per plant over 2 seasons ranged from 3.06 (AL 9l) to 7.41 (BL 3b). Storage root number was significantly higher in Clone BL 3b as compared to both check varieties.

The overall mean performance over 2 seasons revealed higher yield potential of BL 6i (15.89 t ha-1) followed by 5ML 7e (14.27 t ha-1) and BL 3b (14.01 t ha-1). Similarly mean marketable storage root yield over 2 seasons was highest for BL 6i (14.35 t ha-1), followed by BL 3b (12.48 t ha-1) and 5ML 7e (12.34 t ha-1). However, performance of 2 check varieties over 2 seasons for total and marketable storage root yield was comparable and low in contrast to the performance of aforementioned recombinant clones.

Evaluation of leaf and stem scab under field conditions for IET Cycle I & II indicated higher incidence

of disease during Cycle I as compared to Cycle II (Table 4). Check variety �Wanmun� exhibited high susceptibility during season I compared to the season II. A similar trend was also evident for the clones, BL 6i, AL 7h and 5ML 7e, whereas clones, 5ML 11g and AL 9l, and check �Waghi Besta� had higher infestation of disease during Cycle II. Based on overall disease ratings over 2 seasons, clones, Bl 3b and BL 6i exhibited consistently lower levels of the disease incidence compared to better check, Waghi Besta.

Organoleptic evaluation revealed high consumer acceptability of BL 6i, AL 7h, AL 9l and Waghi

Besta as reflected by their highest mean taste scores of 2.6 (Fig. 1). High preference for these clones was closely followed by BL 3b (2.30), Wanmun and 5ML7e (2.20) and 5ML 11g (1.5).

Sweetpotato clone/

cultivar

Sweetpotato scab rating* Mean

IET Cycle I IET Cycle II

5ML 7e 1.75 1.00 1.38

5ML 11g 1.00 1.50 1.25

AL 7h 2.50 1.75 2.13

AL 9l 1.00 2.00 1.50

BL 3b 1.00 1.00 1.00

BL 6i 1.25 1.00 1.13

Waghi Besta (Check) 1.00 1.50 1.25

Wanmun (Check) 3.00 1.00 2.00

Grand mean 1.56 1.34 1.45

LSD at P≤0.05 1.021 1.060

CV (%) 8.0 20.6

P-value 0.002 0.331

Table 4. Sweetpotato scab ratings of early maturing clones recorded during IET Cycle I & II under field conditions

*Average scab ratings on a scale of 1-5, where 1= highly resistant, 2= resistant, 3= moderately resistant, 4= susceptible, 5=highly susceptible.


35

2.2

0

1.5

0

2.6

0

2.6

0

2.2

0

2.3

0

2.6

0

2.6

0

0.00

0.50

1.00

1.50

2.00

2.50

3.00

5ML

7e

5ML

11g

AL 7h

BL 6i

Wan

mun

BL 3b

AL 9l

Wag

hi Bes

ta

Sweet potato clones

Ove

rall

acc

epta

bil

ity

Fig 1. Mean taste scores of the selected clones for culinary traits as tasted by panellists. Average taste preferences based on sensory evaluations of sweetpotato taste acceptability on a scale of 1-4, where 1=least preferred and 4=most preferred by farmers.


DISCUSSION

Sweetpotato is the predominant staple crop of PNG and continuous improvement in its production and productivity is vital for ensuring food security to ever growing population of PNG. Thus it is imperative to have continuous scientific interventions and monitoring of its production systems. However, as reflected by the available reported data, at present the realized productivity is far below its production potential. This in turn is attributed to a complex of many factors including poor soil fertility, lack of improved crop varieties, use of diseased/dirty planting material, and its subsistence crop status. Therefore, the present breeding programme was started in 2005 in an attempt to systematically breed and identify early maturing high yielding sweetpotato clones having better consumer acceptability and broader resistance to important prevalent biotic and abiotic stresses so as to improve its production and productivity in PNG.

A total of 630 genetically recombinant seeds produced in the Crossing Block at farmer�s field level

were taken through different selection stages focussing on early storage root formation and high yield potential coupled with acceptable storage root traits. Six promising elite clones were ultimately identified for intensive testing for yield, quality and culinary traits in the replicated yield trials. Different levels of selection intensities were applied under the present programme including 12.8 per cent at seedling nursery, 31.9 per cent at Hill Trial and 26 per cent at Preliminary Trial stage. Overall 0.48 per cent selection pressure was applied throughout the selection process. A wide range of selection intensities ranging from 10-27 per cent are reported to be used in sweetpotato breeding programmes elsewhere (Wang, 1982; Tumana and Kesavan, 1987). Intense selection pressure exerted under present programme could be attributed to complex breeding objectives including early maturity, yield, storage root morphology, viz. shape, colour, surface texture etc., diseases resistance and culinary traits apart from other natural and/normal selection criteria including seed viability and storage root bearing potential of recombinant progenies.

Evaluation of storage root yield of the selected early maturing recombinant clones and checks over 2

seasons revealed high yield potential of newly bred clones with storage root yields ranging from 10.39 (Wanmun) to 17.12 (BL 6i) t ha-1 and 6.96 (AL 9l) to 16.43 (5ML 7e) t ha-1under IET Cycle I and IET Cycle II, respectively. Similar yields ranging from 2.10 to 12.32 t ha-1 from the evaluation of 30 early maturing

36

sweetpotato genotypes has been reported under Aiyura conditions (Bang et al., 2008). Bourke (1985) had also reported comparable average yields of 5-20 t ha-1 from traditional gardens in PNG. Recombinant clones, BL 6i and BL 3b justified their selection through their high yield potential beating both check varieties, Waghi Besta and Wanmun during season 1. However, under IET II (Season 2) there was decline in the yields of most of the clones. During this season, only clone 5ML 7e could surpass check variety, Waghi Besta. Differential performance of test clones and checks observed over 2 seasons in the present studies can be attributed to GXE interactions. Detailed monthly weather data clearly indicates that Season 2 was comparatively drier and sunnier as compared to season 1 (Table 5). Overall, clones BL 6i, 5ML 7e and BL 3b exhibited high yield potential over 2 seasons which clearly indicated their superiority over existing local commercial varieties. Similar trend was also evident for mean marketable storage root yield. Clones BL 3b and BL 6i yielded more marketable storage roots as compared to best check, Waghi Besta during season 1. During season 2, the performance of clone 5ML 7e was better than check, Waghi Besta. This probably can be attributed to its better adaptability to comparatively drier conditions during season 2 and thus this genotype can be exploited to tackle minor moisture deficiencies during the growing season. Data on storage root number indicated that clones BL 3b, 5ML 7e and BL 6i produced more storage roots, whereas conversely clone AL 7h recorded lower storage root number.

Scoring of the incidence of sweetpotato leaf and stem scab over 2 seasons revealed higher incidence of

sweetpotato leaf and stem scab during Season 1 as compared to season 2 which can easily be attributed to high humidity and wet conditions prevalent during season 1. Sweetpotato scab is known to be favoured by heavy rainfall and humid conditions (Smit et al., 1990). Disease scores clearly indicated lower levels of incidence of scab on BL 3b and BL 6i as compared to best check, Waghi Besta.

Sweetpotato is a staple crop of the PNG smallholders, consumed everyday by its inhabitants and their

taste preferences are thus of paramount importance for successful adoption of new cultivars. Organoleptic evaluation revealed high consumer acceptability for storage roots of BL 6i, AL 7h, AL 9l and Waghi Besta. This was closely followed by BL 3b, 5ML 7e and Wanmun. Dry matter is also known to play crucial role in eating quality of storage roots and clones having dry weights of 30% or higher are known to be preferred in Tonga (Wilson et. al, 1989). Thus acceptable eating quality of the aforementioned clones indirectly reflected their probable better dry matter contents.

Month and year

Rainfall (mm)

Solar Radiation (MJ/m)

Temperature (C°)

Relative Humidity (%)

Evaporation (mm/D)

Total Mean Max. Min. Mean Mean Total

Season 1 (IET Cycle I)

Dec-08 385.6 20.50 26.21 15.73 19.7 80.42 123.86

Jan-09 123.4 25.04 26.23 14.99 19.4 78.28 152.88

Feb-09 233.4 21.75 26.02 15.92 19.4 81.11 115.83

Mar-09 327.6 29.08 25.45 15.15 18.8 83.48 183.27

Apr-09 285.4 27.01 24.99 15.31 18.9 83.30 147.08

Season 2 (IET Cycle II)

May-09 119.2 33.52 25.41 15.29 19.1 81.41 176.14

Jun-09 212.2 38.39 24.63 15.42 18.8 83.30 202.24

Jul-09 150.4 38.24 23.83 15.16 18.2 84.90 204.44

Aug-09 40.2 28.94 24.20 14.79 18.5 81.81 333.99

Sep-09 139.8 30.22 24.92 14.02 18.5 80.73 334.78 Oct-09 142.4 22.58 25.49 13.78 18.6 79.94 442.14

Table 5. Average monthly weather data during crop growing seasons 1 and 2


37

Overall high yielding potential of clones, BL 6i, BL 3b and 5 ML 7e coupled with better resistance of the former two for sweetpotato scab along with medium to high consumer acceptance reflected success of the current breeding programme in ameliorating desirable traits of the parent clones. Based on maturity, yield po-tential, disease resistance and taste, BL 6i was identified as most promising recombinant clone, closely fol-lowed by BL 3b and 5 ML 7e. These 3 clones were hence promoted for evaluation under Advanced Evaluation Trials to further validate their superiority for yield before their testing at farmer�s fields. Once validated, the best bet clones are likely to be released as first locally bred early maturing sweetpotato cultivars of PNG.

REFERENCES Bang, S., Bagle, G., Geob, T., Kapal, D. and Kiara, J. (2008). Early maturing sweet poatato varieties for the

highlands of PNG. Papua New Guinea Journal of Agriculture, Forestry and Fisheries 51: 17-22. Bourke, R. M. (1985). Sweetpotato (Ipomoea batatas) Production and Research in Papua New Guinea. Papua

New Guinea Journal of Agriculture, Forestry and Fisheries 33: 89-108. Bourke, R. M. and Vlassak, V. (2004). Estimates of food crop production in Papua New Guinea. Canberra:

Land Management Group, Department of Human Geography, Research School of Pacific and Asian Studies, The Australian National University.

Fajardo, D. S., Bonte, D. R. La and Jarret, R. L. (2002). Identifying and selecting for genetic diversity in Papua New Guinea sweetpotato Ipomoea batatas (L.) Lam. Germplasm collected as botanical seed. Genetic

Resources and Crop Evolution 49: 463-470. Smit, N. E. J. M, Holo. T. and Wilson, J. E. (1990). Sweetpotato seedling test for resistance to scab disease

(Elsinoe batatas). Tropical Agriculture 68: 263-267. Tumana, C. W. and Kesavan, V. (1987). The evaluation of polycross hybrids. Science in New Guinea 14(3):

132-139. Wang, H. (1982). The breeding of sweet potatoes for human consumption. In: R. L. Villareal and T. D. Griggs

(eds.), In Sweet potato Proceedings of the First International Symposium AVRDC, Tainan, Taiwan:

AVRDC, pp. 297-311. Watson, J. B. (1965). The significance of recent ecological change in the central highlands of New Guinea.

Journal of the Polynesian Society 74: 438-50. Wilson, J. E., Pole, S. F., Smith, N. E. J. M. and Taufatofua, P. (1989). Sweetpotato (Ipomoea batatas) Breed-

ing. Agro-Facts. Institute for Research, Extension and Training in Agriculture Publication No. 89:36-37.


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Volume 2, 39� 47, 2010

POTENTIAL OF NEWLY BRED SWEETPOTATO CLONES AS IMPROVED CULTIVARS UNDER HIGHLAND CONDITIONS OF

PAPUA NEW GUINEA II. Performance of Orange Flesh Sweetpotato Clones

R. K. Kapila*, B. Wera, M. Deros, R. P. Pawilnga, S. Ivahupa1, G. Bagle2, T. Okpul3,

and E. Guaf2 NARI Highlands Regional Centre, P.O Box 384

Aiyura, Eastern Highlands province, Papua New Guinea

ABSTRACT

Sweetpotato (Ipomoea batatas L.) is the single most important staple crop of Papua New Guinea (PNG) and thus needs constant monitoring and technological interventions in its production systems. Under a sweetpotato breeding programme aimed at developing high yielding orange flesh sweetpotato (OFSP) clones, more than four hundred genetically recombinant seeds were generated through a polycross mating among twelve parents. Scarified seeds were germinated and 45 mature plants established from seedlings exhibiting storage root formation potential. Selection intensities ranging from 15-73 per cent with an overall selection pressure of 0.98 per cent were employed at different stages where 4 elite clones, viz. BL 8b, BL 8d, BL 6g and AL 19a were identified. Evaluations of these clones under replicated trials at NARI Highlands Regional Centre, Aiyura revealed higher storage root yield potential of the clones compared to international commercial variety �Beauregard�. Overall storage root yield from two trials during dry and wet seasons ranged from 7.83 to 15.81 t ha-1 under low input subsistence farming practices. All four newly bred recombinant clones exhibited better resistance to sweetpotato scab (Elsinoe batatas) under field conditions as compared to local and exotic cultivars. Carotene content assessment and organoleptic evaluations indicated higher content in clone BL 8b and consumer acceptability of 2 recombinant clones, BL 8b and BL 8d compared to �Beauregard�. Although low in carotene contents, Clone BL 8d also exhibited storage root yield stability under adverse conditions, particularly under dry/minor drought like

conditions. The clones are undergoing further evaluation under advanced trials at present to further validate their potential before their final release as first locally bred Orange fleshed commercial cultivars of PNG. Overall the current breeding programme has been successful in ameliorating desirable traits and generating promising OFSP clones with better yield, nutritive value, eating quality and a degree of resistance to sweet potato scab. Key words: Breeding, Ipomoea batatas (L.), Polycross mating, â-carotene, leaf scab

_________________________________________________________________________________________ *Corresponding author: Tel: +675 537 3500, FAX: +675 537 3516, Email: [email protected] 1Present address: Australian National University Enterprise, PNG LNG Project, Southern Highlands, Papua New Guinea; 2 NARI Momase Regional Centre, PO Box 1639, Lae 411, Morobe Province, Papua New Guinea; 3UNITECH Biotechnology Centre, Agriculture Department, PNG University of Technology, Lae, Morobe Province, Papua New Guinea.

Article received on 10th September, 2010; Accepted after revision on 22nd November, 2010

INTRODUCTION

Sweetpotato (Ipomoea batatas L.) is the single most important staple storage root crop of PNG with an estimated production of 2.9 million tonnes per annum worth an estimated value of US700 millions (Bourke and Vlassak, 2004). It has evolved from a mere pre-colonial introduction in Papua New Guinea highlands to a single major staple food, producing 66 % of food energy for the nation. Heavy dependence on this crop as a staple food has also made the food security of the nation more vulnerable to the potential biotic and abiotic threats in the long run. Therefore, this situation warrants regular monitoring of the crop production systems through planned and continuous agro-technological interventions.


Despite its importance, the productivity is low due to factors such as low yielding cultivars, susceptibility to pests and diseases, poor soil fertility and poor agro-technological interventions including use of poor quality planting material by farmers. Furthermore, their genetic base is feared to be very narrow, imposing its broadening by including appropriate diverse cultivars in the breeding program as a safeguard against potential threats, although there are large genetic resources of sweet potato in the form of landraces (Fajardo et al., 2002). Broadening of the genetic base also becomes relevant in face of the threats imposed by climate change. Among known malnutrition, Vitamin A deficiency (VAD) is important globally, and can cause blindness apart from reduced immunity in the body. PNG has been classified by the World Health Organisation as an area where clinical VAD exist.

Sweetpotato is naturally a rich source of carbohydrates and vitamin A, and development and/

identification of carotene dense, orange flesh sweetpotato (OFSP) clones can help in combating VAD. However, the available OFSP (s) tend (s) to have low dry matter accompanied by low yield and lack of resistance against pests and diseases, and thus are not very popular with the consumers (Tomlins et al., 2004). Therefore, this study was undertaken aiming at genetic improvement of carotene rich genotypes for yield, taste acceptability and other agronomic traits to potentially improve food security and to combat VAD in rural PNG through their production and consumption.

MATERIALS AND METHODS

Twelve elite clones of sweetpotato were selected from germplasm collections as potential parents based on their desirable traits including high storage root yield, early maturity, tolerance to drought, flesh colour (orange), flowering ability and other desirable horticultural traits, and raised in a polycross mating design under a farmers� participatory breeding program (Table 1). Random cross pollination among parents was promoted by staking them on inverted �V� shaped structures to encourage flowering and to expose flowers of all parents equally to visiting pollinators. Genetically recombinant true half-sib seeds set on each parental clone were collected after flowering season.

No. Cultivar/Clone Type Source

1 PRAP 469 1DT/2EM 4PRAP

2 SSYK 026 DT/EM 5HSPG






8 SKK 010 DT/EM PRAP

9 WBS 010 DT/EM PRAP

10 Top 20/Kerot Hagen 3OFSP 6Local

11 2 Kina anta DT/EM Local 12 Maraso DT/EM Local

Table 1. Promising parent clones involved in a polycross mating block under farmers� participatory breeding program and their prominent desirable traits

1Drought tolerant; 2Early maturing; 3Orange Flesh Sweetpotato; 4Pacific Regional Agricultural Programme; 5Highlands Sweetpotato Germplasm;

Niugini Agrisaiens 2, 39-47, 2010 Potential of orange flesh sweetpotato clones Kapila et al.

40

Properly filled mature seeds were scarified manually using scalpels to break hard seed coat and soaked in water for 48 hours before transfer to the nursery bed. The nursery bed contained sterilized medium of three parts top soil, two parts sand and one part of chicken manure. The seeds were sown at 4 and 5 cm plant to plant and row to row spacing, respectively. After three months, seedlings exhibiting storage root formation potential were selected in the nursery and advanced for further field screening and evaluation, on single cycle of hill and preliminary trials, and two replicated Initial Evaluation Trials (IETs) in 2 separate growing seasons. Further evaluation of these clones in two Advanced Evaluation Trials (AETs) is under progress. The selected clones were planted on single hill at a spacing of 1m (row to row and plant to plant). Observations were made on growth habit, pest and disease incidences, earliness to maturity, yield, storage root shape and quality. Those clones exhibiting desirable traits were selected with active participation of farmers. Selection at harvest was based on the following criteria: storage root shape, flesh colour (Orange flesh), storage root skin texture, size distribution, storage root number and observable diseases or defects. Selected OFSP clones were advanced for evaluation under Preliminary Trial using the same criteria and potential clones evaluated further under replicated IETs. All activities involved in the screening and selection of new polycross clones were based at NARI Highlands Research Centre�s Farm at Aiyura located 145.90° E and 06.35° S at an altitude 1660 m above sea level, except for the nursery selection. Selected clones in the initial trials were planted in a Randomised Complete Block Design with four replicates (RCBD) at a spacing of 1m between plants and rows with a net plot size of 4m2. The first initial trial comprised two newly bred clones as treatment while Cycle 2 evaluation included four newly bred clones along with 3 potential local cultivars (Kerot Goroka, AIYIB 657 and PRAP Minz). An Australian commercial cultivar �Beauregard� was used as standard check to compare performance of newly bred local OFSP clones. No chemical fertilizers and pesticides were used in these trials. Other optimum conditions of management were maintained throughout the cropping period with manual weeding done twice during the crop growing season. IET Cycle I trial was planted on 17th December, 2008 and harvested on 29th April 2009, whereas IET Cycle II was planted on 20th May, 2009 and harvested on 26th October, 2009.

Sweetpotato leaf and stem scab disease (Elsinoe batatas [Saw.] Viegas and Jenkins) assessment was done at two weeks interval throughout the cropping season after planting based on visual observation on the selected plants. For each sample plant, disease severity was scored and recorded on a scale from 1-5 as a reflection of per cent of leaf and/ stem area affected by scab. The scale is described as 1- highly resistant (0 % damage), 2 � resistant (1-25% damage), 3 � moderately resistant (26-50% damage), 4 � susceptible (51-75% damage) and 5 � highly susceptible (>75% damage).

The IETs were harvested after maturity of majority of the clones at least four months after planting.

All underground parts/storage roots were cleared from adhered soils or debris. The storage roots were separated into marketable edible storage roots (>100g, i.e. 180-250mm length & 60-75mm diameter) and non-marketable storage roots (<100g i.e. 130-180mm in length and 50-60mm diameter). The total number of storage roots and fresh weights of the above categorized storage roots were recorded accordingly for each plot.

Assessment of OFSP clones for carotenoid level was done by comparing colour of storage root flesh

to Standard Carotenoid Colour Chart selectively designed for sweetpotato and other storage root crops by HarvestPlus programme of the Consultative Group on International Agricultural Research (CGIAR). Fleshes of 5 randomly selected OFSP storage roots from each entry were sliced open to expose their natural flesh colours under day light. Carotenoid Colour Chart was compared against the respective excised progeny storage roots to ensure their approximate carotenoid reflection. The approximate carotenoid content in the standard colour strips were given specific codes to which matching of orange flesh storage roots were done accordingly.

41


Storage root colour intensity that best matched the Standard Colour Chart were averaged and recorded. On the HarvestPlus Carotenoid Color Chart of 1-4, 1= RHS: 5/3 7401U light orange, 2= RHS: 9/3 7507U intermediate orange, 3= RHS: 9/2 1355U orange, 4= RHS: 9 137U dark orange flesh colour reflected level of carotene contents in ascending order.

Sensory evaluation for culinary traits of sweetpotato was done through organoleptic evaluation.

General appearance, odour, colour, softness, taste, chewiness, sweetness, mealiness, stickiness, fibre content and overall acceptability of cooked storage roots of each clone were assessed by the panellists. The panel comprised of more than 10 tasters, evaluated the taste of roasted (dry mumu) storage roots. Storage roots of all clones were subjected to only one most common cooking method (dry mumu) and were sliced into 5 cm x 5 cm pieces when cooked. Without knowing their actual identity, the samples were respectively and randomly assembled on the table with temporary codes on them. Each panellist had a chance to taste at least all the samples coming from each clone and score according to his/her own judgment on a 1-4 scale, where 1=least preferred and 4=most preferred. The panellists� overall impressions were computed by adding all the weighted numbers and were then averaged and presented in the result.

The data collected on yield and component traits, and disease severities were subjected to analysis of

variance (ANOVA) using Statistical Analysis Procedures (Genstat Version 3). Fisher�s protected least significant difference (LSD) test was used to detect differences between means of the clones. RESULTS The twelve (12) parental clones varied in vegetative, floral and storage root characteristics. There was also variation shown in seed production and germination rate, and in production of potential storage root bearing progenies. Overall more than four hundred recombinant seeds were harvested from the polycross block, out of which three hundred were planted in nursery. All recombinant clones were subjected to intensive selection pressure afterwards, based on the breeding objectives. Based on observable storage root formation potential, about 15 % of the total germinated seedlings in the nursery were selected for single hill trial where 35.5 % of aforementioned selections were further advanced for evaluation under Preliminary Trial (Table 2). Out of the clones evaluated under Preliminary Trial, 4 (25 %) were promoted for further yield evaluations. Overall 0.98 per cent of the total recombinant progenies harvested at seed level ultimately made it to the replicated trials.

Evaluation of selected recombinant OFSP clones under IETs revealed that mean marketable and total

storage root yield for check �Beauregard� was numerically highest but statistically at par with 2 recombinant OFSP clones, BL 8d and BL 6g in the first trial season (Table 3). Overall mean storage root yield ranged from 13.84 to 16.88 t ha-1. Similarly total storage root number per plant was also recorded highest for check variety (9.88), followed by clones BL 6g and BL 8d. Under IET Cycle II which involved 2 additional recombinant clones and 3 local popular varieties, the total storage root yield ranged from 4.20 (Beauregard) to 15.81 t ha-1

(BL 8d). Amongst the test cultivars, total storage root yield was higher in 3 recombinant clones (BL 8d, BL 8b & AL 19a) and 2 local varieties (Kerot Goroka and PRAP Minz) as compared to the check. Within recombinant clones, the performance of BL 8d and BL 8b was significantly superior to the check �Beauregard� and other recombinant clone, BL 6g. Recombinant clone, AL 19a performed better than check but was at par statistically with BL 6g and BL 8b. Among local cultivars, Kerot Goroka performed better and its total yield was at par with 2 high yielding recombinant clones, BL 8d and BL 8b. Similar trend was also evident for mean marketable storage root yield with superiority of BL 8d over the check and other recombinant clones (BL 6g and AL 19a) and local cultivar (AIYIB 657). Mean storage root number under IET Cycle II ranged from 5.44 (Kerot Goroka) to 9.25 (BL 8b). In general more storage root number per plant was recorded under IET Cycle II as compared to Cycle I, except for check �Beauregard�. Amongst recombinant clones and local cultivars evaluated, storage root number was higher in BL 8b and AIYIB 657 as compared to local cultivar Kerot

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Breeding Stage Selection Criterion(a) Total progenies produced/ evaluated

Number of progenies selected/ advanced

Selection intensity (%)

Crossing Block (CB) Proper seed development

410 300 73.17

Seedling Nursery (SN) Storage root formation potential of seedlings

300 45 15.0

Hill Trial (HT) Storage root shape colour, number, yield and pest and diseases

45 16 35.5

Preliminary Trial (PT) Storage root shape colour, number, total yield , pest and diseases, and taste

16 4 25.0

Initial Evaluation Trial (IET 1 & 2)

Yield potential, culinary traits and pest and diseases incidence

4 4 100.0

Overall selection % 410 4 0.98

Table 2. Total population of recombinant progenies and selection intensities employed at different stages of OFSP breeding program

Mean storage root number per plant

Mean marketable storage root yield1 (t ha-1)

Mean total storage root yield1 (t ha-1)

IET Cycle 1

IET Cycle 2

IET Cycle 1

IET Cycle 2

IET Cycle 1

IET Cycle 2

BL 8d 6.56 7.06 13.06 14.66 13.96 15.81

BL 8b * 9.25 * 11.22 * 13.51

BL 6g 7.62 8.69 12.02 4.93 13.84 7.83

AL 19a * 7.88 * 9.01 * 10.64

Kerot Goroka * 5.44 * 9.73 * 12.73

AIYIB 657 * 9.12 * 6.01 * 8.91

Prap Minj * 6.06 * 9.72 * 10.84

Beauregard (Check)

9.88 6.62 14.48 2.67 16.88 4.20

Grand mean 5.59 7.52 8.93 8.49 10.35 10.56

LSD 1.733 3.326 4.797 5.278 4.689 5.190

CV (%) 8.3 13.4 12.4 32.3 9.8 26.5

P-value <0.001 0.183 <0.001 0.003 <0.001 0.005

1Yield based on a plot area = 4m2 * Not evaluated under IET Cycle I

Table 3. Performance of selected recombinant elite OFSP clones for storage root yield and its component traits under IET Cycles I & II

Incidence of leaf and stem scab, and its scoring under field conditions under IET Cycle I & II revealed higher susceptibility of check (Beauregard) and local varieties (Kerot Goroka, AIYIB 657 and Prap Minj) under prevalent field conditions at Aiyura in contrast to new recombinant clones under evaluation which had lower incidence of disease (Table 4). Check variety �Beauregard� exhibited high susceptibility during Season I compared to the Season II. Reaction of new clones was comparatively almost consistent over seasons.

43


Assessment of carotene content through colour comparisons with HarvestPlus Colour Chart indicated Beauregard and recombinant clone, BL 8b to be rich in carotene contents as reflected by their flesh colour scores of 4+ and 4, respectively. Local cultivars had moderately high (Prap Minj) to moderately low contents (Kerot Goroka and AIYIB 657) with scores of 3 and 2, respectively, whereas carotene contents in other 3 new recombinant clones, except BL 8b were assessed to be moderately low to low (Table 4).

Sweetpotato clone

Mean leaf & stem scab scores

Carotenoid colour codes

Carotenoid Content Level

IET Cycle 1

IET Cycle 2

IET Cycle 2

IET Cycle 2

BL 8d 2.0 1.00 RHS:5/3 7401U 1 = low

BL 8b * 1.25 RHS:9 137U 4 = high

BL 6g 1.0 1.00 RHS:9/3 7507U 2 = moderately low

AL 19a * 1.00 RHS:9/3 7507U 2 = moderately low

Kerot Goroka * 3.00 RHS:9/3 7507U 2 = moderately low

AIYIB 657 * 3.75 RHS:9/3 7507U 2 = moderately low

Prap Minj * 2.75 RHS:9/2 1355U 3 = moderately high

Beauregard 4.25 1.00 RHS:9 137U 4+ = very high

Grand mean 3.22 1.84

LSD 1.358 1.023 CV (%) 16.0 16.0

P-value <.001 <.001

Table 4. Assessment of sweetpotato scab resistance/susceptibility under field conditions and carotene content of OFSP clones under IET Cycle I & II

* Not evaluated under IET Cycle I

2.2

1.9 2.1 2

.4

1.6

2.3 2.4

2.4

0

0.5

1

1.5

2

2.5

3

Kerot

Gor

oka

AIYIB

657

BL 8d

AL 19

a

Beaur

egar

dBL

6g

BL 8b

Prap

Minj

Sweet potato clones

Ove

rall

acce

ptab

ility

Fig 1. Mean taste scores of the selected OFSP clones for culinary traits as tasted by

panelists. Average taste preferences based on sensory evaluations of sweetpotato

acceptability with scale of 1-4, where 1=least preferred and 4=most preferred by

farmers.

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Assessment of culinary traits and farmer�s taste acceptability studies through panel tasting revealed high consumer acceptability of PRAP Minz, AL 19a and BL 8b as reflected by their highest mean taste scores of 2.4 (Fig 1). Interestingly all 4 newly bred OFSP clones exhibited high preference with farmers for their taste with scores ranging from 2.1 (BL 8d), 2.3 (BL 6g) to 2.4 (BL 8b and AL 19a). Exotic check cultivar �Beauregard� was least preferred with a score of 1.6. The other two local cultivars exhibited moderate acceptability with scores of 1.9 and 2.2 for AIYIB 657 and Kerot Goroka, respectively.

DISCUSSION Sweetpotato is the most important staple crop of PNG and hence requires continuous scientific interventions and monitoring of its production systems so as to ensure food and nutritional security to the smallholders of the country. However, as reflected by the available data, the crop productivity is low and is further declining due to complex of many factors including poor soil fertility, lack of improved crop varieties and availability of clean planting material. Therefore, the present programme was started in 2005 in an attempt to systematically breed and identify high yielding OFSP clones with better consumer acceptability and broader resistance to important prevalent diseases.

The twelve selected parental clones exhibited variation in vegetative, floral and storage root characteristics as well as in seed production, seed germination and production potential of storage root bearing progenies. Progenies advanced from a total of 410 recombinant seeds, were taken through different selection stages and ultimately 4 promising elite clones were identified for intensive testing for yield, quality and culinary traits in the replicated yield trials. Selection intensities applied under the present programme included 15 per cent at seedling nursery, 35.5 per cent at Hill Trial and 25 per cent at Preliminary Trial stage. Overall 0.98 per cent selection pressure was applied at various stages depending upon breeding objectives which is more intense than reported elsewhere. Selection intensities less than 10 % have been generally used by the Asian Vegetable Research Development Centre (AVRDC), but under such intensities, some desirable genotypes were lost (Wang, 1982). Tumana and Kesavan (1987) had also reported practising 27 per cent selection intensities. Under the present programme, intense selection pressure exerted could be attributed to complex breeding objectives including storage root morphology, viz. shape, colour, surface texture etc., carotene contents, diseases resistance, culinary traits and yield levels in addition to other criteria including seed viability and storage root formation potential. Evaluation of storage root yield of the selected recombinant OFSP clones along with local cultivars and check under IET Cycle I & II revealed high yield potential with storage root yields ranging from 13.84 to 16.88 t ha-1 and 7.83 to 15.81 t ha-1, under IET Cycle I and IET Cycle II, respectively. Bang et al. (2008) also reported comparable average yields ranging from 2.10 to 12.32 t ha-1 from the evaluation of 30 early maturing sweetpotato genotypes under Aiyura conditions. However, higher experimental yields of 6.3 to 49.6 t ha-1 from progenies obtained from parental clones of

PNG lowlands sweetpotato have also been reported by Ernest et al. (1994). In this study, yields of 2 new

recombinant clones, BL 8d and BL 6g was comparable and at par with high yield potential exhibited by Australian commercial variety �Beauregard� used as check during Season 1 evaluation. However, under IET II (Season 2), check variety �Beauregard� and recombinant clone, BL 6g exhibited steep decline in yields, whereas performance of clone, BL 8d was stable. This probably could be attributed to GXE interactions. Detailed monthly weather data clearly indicates that Season 1 had higher and more uniformly distributed rains, whereas season 2 was comparatively dry and sunnier, particularly at the time of trial establishment (Table 5). As noticed during trial establishment, replanting of few mounds was forced in case of �Beauregard� as its cuttings, planted at the beginning, were not able to establish due to lack of enough moisture indicating its inability to adapt to the prevalent dry conditions. Similar was true for BL 6g also. Overall, clones BL 8d, BL 8b and AL 19a along with local cultivars Kerot Goroka and PRAP Minz exhibited high yield potential during IET II. Similar trend was evident for mean marketable storage root yield which was recorded highest and stable for recombinant clone BL 8d. Consistencies in the performance of BL 8d as compared to BL 6g and Beauregard across two contrasting seasons clearly indicates its better yield stability and high yield potential during dry season.

45


Table 5. Average monthly weather data during crop growing seasons 1 and 2

Month and year

Rainfall (mm)

Solar Radiation (MJ/m)

Temperature (C°)

Relative Humidity (%)

Evaporation (mm/D)

Total Mean Max. Min. Mean Mean Total

Season 1 (IET Cycle I)

Dec-08 385.6 20.50 26.21 15.73 19.7 80.42 123.86 Jan-09 123.4 25.04 26.23 14.99 19.4 78.28 152.88 Feb-09 233.4 21.75 26.02 15.92 19.4 81.11 115.83 Mar-09 327.6 29.08 25.45 15.15 18.8 83.48 183.27 Apr-09 285.4 27.01 24.99 15.31 18.9 83.30 147.08

Season 2 (IET Cycle II) May-09 119.2 33.52 25.41 15.29 19.1 81.41 176.14 Jun-09 212.2 38.39 24.63 15.42 18.8 83.30 202.24 Jul-09 150.4 38.24 23.83 15.16 18.2 84.90 204.44 Aug-09 40.2 28.94 24.20 14.79 18.5 81.81 333.99 Sep-09 139.8 30.22 24.92 14.02 18.5 80.73 334.78 Oct-09 142.4 22.58 25.49 13.78 18.6 79.94 442.14

Thus such clones can be useful in tackling minor moisture deficiencies/drought during the growing season, occurrence of which is quite common and frequent in PNG.

Scoring of the incidence of sweetpotato leaf and stem scab over 2 seasons further validated different

prevailing climatic conditions. Incidence of sweetpotato leaf and stem scab was more intense during Season 1 compared to season 2. This is understandable as the disease is known to be favoured by heavy rainfall and humid conditions (Smit et al., 1990). Disease scoring clearly indicated the higher susceptibility of exotic check and local varieties as compared to newly generated OFSP clones. Clones BL 6g, BL 8b and BL 8d, apart from exhibiting higher yield potential were scored as highly resistant to resistant indicating their potential in management of this disease.

Sweetpotato is a staple crop of PNG smallholders and preference of consumers for specific taste is

thus of paramount importance for successful adoption of new cultivars. Assessment of carotene contents and organoleptic evaluation revealed moderately high to moderately low carotenoid contents in 3 local cultivars and in 2 of the 4 newly generated OFSP clones, whereas Beauregard and clone, BL 8b were assessed to have high contents. Generally clones with high dry matter are known to be preferred by consumers in PNG. Per cent dry matter is a good measure of eating quality, hence clones having dry weights of 30% or higher is mostly preferred in Tonga also (Wilson et. al, 1989). Recombinant clones BL 8d, BL 8b and BL 6g apart from having higher yield potential and disease resistance also exhibited taste acceptability with farmers which were quite a reflection of the success of present breeding programme. Besides, some of the clones/cultivars exhibiting low storage root number give higher yield and some even have high storage root number giving low yield. That means, some of the high yielding varieties produce less number of bigger sized storage roots whereas the opposite is also true. Clone BL 8d can be regarded as producing medium sized storage roots with higher yield which can be favoured by consumers/markets.

Overall the current breeding programme has been successful in ameliorating desirable traits and has

generated promising recombinant clones having high yield potential coupled with a degree of resistance to sweetpotato scab and better consumer acceptability. At present, yield potential and other traits are being further validated in Advanced Evaluation Trials. Once validated, the promising clones are likely to be released as first locally bred orange fleshed sweetpotato cultivars of PNG.

46


Acknowledgement Initial financial support by the Agricultural Innovative Grant Facility (AIGF) of AusAID towards the farmer participatory sweetpotato breeding is acknowledged. The authors are also grateful to the cooperation of farmers Messrs Figiman Marike, Behem Malku and Albert Tivaku and duly acknowledge guidance and support provided by PNG National Agricultural Research Institute�s management during conduct of the present study.

REFERENCES Bang, S., Bagle, G., Geob, T., Kapal, D. and Kiara, J. (2008). Early maturing sweet poatato varieties for the

highlands of PNG. Papua New Guinea Journal of Agriculture, Forestry and Fisheries 51: 17-22. Bourke, R. M. and Vlassak, V. (2004). Estimates of food crop production in Papua New Guinea. Canberra:

Land Management Group, Department of Human Geography, Research School of Pacific and Asian Studies, The Australian National University.

Ernest, J., Wagih, I. E., Kesavan, V. (1994). Genetic evaluation of polycross hybrids of sweetpotatoes. African

Crop Science Journal 2: 29-34. Fajardo, D. S., Bonte, D. R. La and Jarret, R. L. (2002). Identifying and selecting for genetic diversity in Papua

New Guinea sweetpotato Ipomoea batatas (L.) Lam. Germplasm collected as botanical seed. Genetic

Resources and Crop Evolution 49: 463-470. Smit, N. E. J. M, Holo. T. and Wilson, J. E. (1990). Sweetpotato seedling test for resistance to scab disease

(Elsinoe batatas). Tropical Agriculture 68: 263-267. Tomlins, K., Rwiza, E., Nyango, A., Amour, R., Ngendello, T., Kapinga, R., Rees, D. and Jolliffe, F. (2004).

The use of sensory evaluation and consumer preference for the selection of sweetpotato cultivars in east

Africa. Journal of the Science of Food and Agriculture 84: 791-799. Tumana, C. W. and Kesavan, V. (1987). The evaluation of polycross hybrids. Science in New Guinea 14: 132-

139. Wang, H. (1982). The breeding of sweet potatoes for human consumption. In: R. L. Villareal and T. D. Griggs

(eds.), In Sweet potato Proceedings of the First International Symposium AVRDC, Tainan, Taiwan:

AVRDC, pp. 297-311. Wilson, J. E., Pole, S. F., Smith, N. E. J. M. and Taufatofua, P. (1989). Sweetpotato (Ipomoea batatas)

Breeding. Agro-Facts. Institute for Research, Extension and Training in Agriculture Publication No. 89:36-37.

47


ACKNOWLEDGEMENT TO REVIEWERS Niugini Agrisaiens acknowledges valuable inputs and services from the following reviewers.

Prof. Biman Chand Prasad Professor of Economics, Dean of Faculty of Business and Economics & Chair of Oceania Development Network Faculty of Business and Economics The University of the South Pacific Private Mail Bag, Suva, Fiji Islands Email: [email protected] Prof. A. Halim Professor and Head Department of Agriculture Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected] Prof. G. Rahman Professor and Head Department of Languages and Communication Studies Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected] Dr. Q. Parvez School of Natural Sciences, K2 Hawkesbury Campus University of Western Sydney Locked bag 1797, NSW 1797 Australia Email: [email protected] Dr. Birte Komolong Principal Scientist (Plant Pathology) National Agricultural Research Institute Bubia, Lae Papua New Guinea Email: [email protected]

Dr. R. K. Kapila Principal Scientist (Crop breeding) NARI Highlands Program, Aiyura Valley P.O. Box 384, Kainantu, Eastern Highlands Papua New Guinea Email: [email protected] Dr. M. Wamala Department of Agriculture Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected] Mr. M. Maino Department of Agriculture Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected] Prof. T. N. Prakash Kammaradi Professor of Agricultural Economics University of Agricultural Sciences GKVK, Bangalore 560065, India Email: [email protected] Mr. P. I. Moorower Department of Business Studies Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected] Mr. P. Michael Department of Agriculture Private Mail Bag Papua New Guinea University of Technology Lae, 411, Papua New Guinea Email: [email protected]












NOTES FOR CONTRIBUTORS AIMS AND SCOPE Niugini Agrisaiens is a peer reviewed research journal, published by the Department of Agriculture, PNG University of Technology, in yearly volumes.

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(Psophocarpus tetragonalobus (L.) DC.) Niugini Agrisaiens 2: 1 � 6. Chartier, P. and Catsky, J. (1999). Photosynthetic systems: conclusions. In Photosynthesis and productivity in

different environments, 425 � 433 (Ed J.P. Cooper). Cambridge: Cambridge University Press. Milthorpe, F.L. and Moorby, J. (2009). An Introduction to Crop Physiology. Cambridge: Cambridge University Press. Not more than fifteen papers should normally be cited, except in invited reviews. If the list is not in the correct format, it will be returned to the author (s) for amendment, and publication of the paper may be delayed. The Editor will not check references: this is the responsibility of authors. Reprints

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