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Project Report On

Studies on the use of Plant Activator and Silicon nutrient for the management of Powdery mildew of Black gram (Vigna mungo L. Hepper)

Submitted by

S.Parthasarathy, Reg. No. 08281 Final B.Sc. (Agri.)

Department of Plant Pathology

Faculty of Agriculture

Annamalai University

Annamalai nagar – 608 002.

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ANNAMALAI UNIVERSITY FACULTY OF AGRICULTURE

DEPARTMENT OF PLANT PATHOLOGY

RES 423 – RESEARCH PROJECT

CERTIFICATE

IV B.Sc.(Agri.) 2011-2012 Final Semester

Certified that Selvan S.Parthasarathy,Reg.No.08281 of IV B.Sc. (Agri.) class has duly completed and submitted a research project entitled “Studies on the use of plant activator and silicon nutrient for the management of Powdery mildew of Black gram (Vigna mungo L. Hepper) ” under my supervision during the final semester of 2011-2012.

Date : Examiners Guide

Place:

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Acknowledgement

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ACKNOWLEDGEMENT

Above all, I submit my thoughts and actions to the Almighty who always guides me in the path of righteousness and whose blessings have enabled me to complete this work successfully.

I have immense pleasure in placing in record my indebtedness and profound sense of gratitude to my guide Dr.V.Jaiganesh, Assistant Professor (Plant Pathology), Faculty of Agriculture, Annamalai University for suggesting this project and for his keen interest, constant encouragement, precise guidance, and constructive criticisms throughout the tenure of this study and the preparation of this dissertation.

I wish to express my heartful thanks to Dr. V. Kurucheve, Ph.D., Professor and Head, Department of Plant Pathology for his generous encouragement during my course of study.

I proudly record my sincere thanks to Dr. RM. Kathiresan, Ph.D.,D.Sc., Dean, Faculty of Agriculture, Annamalai University for allotting my project work in the Department of Plant Pathology and his guidance.

I convey my special thanks to Dr .L.D.C. Henry, and also each and every staff of department of Plant pathology.

On a personal note, I also express my special thanks to Dr.C.Kannan for his immense help during crucial times of need.

With abundance of my heart, I express my affectionate gratitude to my Parents Mr. P.Seethapathy and Mrs. S.Gandhimathi who always stand beside me with moral support and fathomless love in every step of my life.

Place: Annamalai Nagar (S.PATHASARATHY)

Date:

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CONTENTS

Chapter No.

Title

Page No.

1.

2.

3.

4.

5.

6.

7.

8.

Introduction

Review of literature

Materials and Methods

Experimental Results

Discussion

Summary

References

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12

23

28

37

39

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Introduction

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INTRODUCTION

Pulses have been cultivated as protein sources, under low input

agriculture for thousands of years. Pulses constitute the main sources of

essential protein and for predominantly vegetarian population of India.

Among these black gram or urd bean (Vigna mungo L. Hepper) is pulse crop

of many Asian countries and it belongs to tribe phaseolus family

leguminoseae with chromosome number 2n=22. Urd is said to have

originated in India when it is most widely grown and highly esteemed grain

legume (Chatterjee and Bhattacharya, 1986). Black gram attracts high price

among all pulses and it is highly rich in phosphoric acid. It is more often

used for preparing pappad which is a very popular side dish with any kind

of meal, routine or special. Urd bean occupies about 14 per cent of the total

area under pulse in the country and ranks fourth in area and production

after chickpea, pigeonpea and mungbean.

In India alone it occupies about 3.17 million hectare and annual

production of urd bean in India is about 1.33 million tonnes. Urd is highly

prized pulse and cultivated under a wide range of predominantly rain fed

farming system in dry and intermediate agro ecological zones on marginal

lands with low moisture and fertility conditions. Besides it is a important

protein source for people in the cereal-based society because it is rich in

phosphoric acid among pulses, rich in source of vegetable protein (20- 25%)

with some essential minerals and vitamins for the human body.

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Pulses has been under cultivation from time immemorial, being grown

under varying climatic conditions in different parts of the country. It is

widely affected by quite a number of diseases caused by fungi, bacteria,

viruses and mycoplasma which results in higher yield losses (Rangaswami

and Mahadevan, 2005).

Among the fungal diseases, powdery mildew incited by

Erysiphe polygoni DC is a major disease occurring in almost all the black

gram growing areas of the world and is the most destructive fungal disease

of black gram causing yield loss up to 20-40 per cent (Reddy et al., 1994)

despite decades of research towards its management.

The management of powdery mildew disease is done by using

fungicides, growing resistant varieties, balanced nutrition, biological agents

and resistance inducing chemicals. The extraordinary use of chemical

fungicides resulted in environmental pollution and ill health to biotic

community as a whole. Also, the biological method of plant disease

management have not been seems to better alternative to chemical

fungicides in managing the powdery mildew disease. So, a need was felt to

develop novel, more effective and sustainable disease management programs

which do not harm the environment at the same time increase yield and

improve product quality (Dordas, 2008).

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In addition to balanced nutrition, induced resistance by chemicals

may provide an efficient approach to plant protection especially for problems

not satisfactorily controlled by various fungicides (Schoenbeck et al., 1980;

Schoenbeck, 1996). Resistant inducing chemicals are known as inducers of

phytoalexins and/or elicitors of resistance in different plant species (Biswas

et al., 2008; Shabana et al., 2008; Hadi and Balali, 2010). Several chemicals

viz., Salicylic acid (Sarwar et al., 2011), Acibenzolar – S – Methyl (Bengtsson

et al., 2008), Acetyl Salicylic acid (White, 1979), Nicotinic acid (Jaiganesh,

2005), Jasmonic acid (Cohen et al., 1993) and Oxalic acid (Toal and Jones,

1999) have shown induced resistance in various crops.

Besides, a promising alternative for the control for many foliar

diseases, including powdery mildew, is the application of silicon (Si) to soils

deficient in this element (Datnoff et al., 2007). In recent years, silicon (Si) is

being used for the control of fungal diseases with promising results (Yanar

et al., 2011) and silicon accumulation has been reported to be one of the

main factors responsible for enhanced resistance against various pathogens

of different crops (Junior et al., 2009).

Therefore, with an aim to develop an integrated strategy involving the

use of certain resistance inducing chemicals and silicon based nutrients for

the successful sustainable management of black gram powdery mildew, the

present study was undertaken with the following objectives,

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1. To study the effect of individual and combined application of the

resistance inducing chemical and silicon based nutrient for the effective

management of black gram powdery mildew

2. To study the effect due to individual and combined application of the

resistance inducing chemical and silicon based nutrient on enzymatic

changes in black gram plants as influenced by E.polygoni.

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Review of literature

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Review of Literature

Disease importance

The powdery mildew disease, caused by Erysiphe polygoni DC., occurs every

year in the entire rice fallow area under black gram in the Cauvery delta Powdery mildew are

known to develop and spread when temperatures are high (above 30"C) and rainfall is low

with high humidity (Mittal and Sharma, 1992 Abbaiah, 1993 and Raguchander and Rajappan,

1995).

Symptomatology (Rangaswami, 1998)

1. White powdery patches appear on leaves and other green parts which later become dull

coloured. These patches gradually increase in size and become circular covering the

lower surface also.

2. When the infection is severe, both the surfaces of the leaves are completely covered by

whitish powdery growth. Severely affected parts get shrivelled and distorted.

3. In severe infections, foliage becomes yellow causing premature defoliation. The disease

also creates forced maturity of the infected plants which results in heavy yield losses.

4. The pathogen has a wide host range and survives in oidial form on various hosts in off-

season.

5. Secondary spread is through air-borne oidia produced in the season.

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Management

Locke (1990) obsetved that spraying crude oil gave essentially cent per cent control

of powdery mildew on Hydrangeas in Green house better than Benlate (Benomyl). Sulphur

fungicides for commonly recommended for the management of powdery mildew of black

gram (Mohan and Ramakrishnan, 1991). Rettinasasababady et al., (2000) stated that neem

oil is used to controlling the powdery mildew disease with 74.50 per cent.

Induced disease resistance in plants by chemicals

An emerging strategy in plant protection is the induction of systemic acquired

resistance (Lucas, 1999). The phenomenon of induced resistance has been variously

described as systemic acquired resistance (SAR) and induced systemic resistance (ISR) or as

three types of induced resistance: systemic acquired resistance (SAR), induced systemic

resistance (ISR), and wound-induced resistance (Walters, 2009). Systemic acquired resistance

(SAR) inducers can be chemical compounds, metabolites of the host plant, which induce

plant resistance through activation of a plant’s signalling pathways such as the salicylic acid

pathway (Achuo et al., 2004).

The term ‘systemic’ stressing the point that protection is not confined to treated plant

parts but extends to non-treated, an often even newly developing, plant parts

(Hammerschmidt et al., 2001; Metraux et al., 2002). Plants can be induced to develop

improved resistance to plant pathogens with a variety of living and non living inducers. The

resistance induced is wide range and can be long term, but rarely provides complete disease

management (Walters, 2009).

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In dicots the biological induction of the SAR response by localized infections with

necrogenic pathogens is associated with the systemic accumulation of resistance inducing

chemical and certain pathogenesis – related (PR) proteins (Sticher et al., 1997). In monocots

SAR can be chemically activated by the same chemicals as in dicots (Sisler and Ragsdale,

1995; Sticher et al., 1997; Lyon and Newton, 1999) which suggests that the key parts of the

target area in the SAR signaling pathway are also conserved in monocots. Chemical

activators can elicit SAR, which involves a specific set of genes, including those encoding

pathogenesis-related (PR) proteins and enzymes (Durrant and Dong, 2004).

Reports are available on the effectiveness of naturally occurring and synthetic

chemical compounds as abiotic inducers of resistance in susceptible plants. Studies have

shown that SAR is induced in several plant species by treatment with chemicals such as

salicylic acid, methyl-2,6-dichloroisonicotinic acid (INA) or benzo(1,2,3)thiadiazole-7-

carbothionic acid S-methyl ester (BTH) (Hammerschmidt et al., 2001).

Acibenzolar-S-methyl (enzo(1,2,3) thiadiazole-7-carbothioic acid S-methyl ester),

referred to as ASM, is a synthetic molecule from Novartis whose role as a plant defence

activator has been demonstrated in a number of crops including Arabidopsis (Lawton et al.,

1996), tobacco (Friedrich et al., 1996), wheat (Gorlach et al., 1996), bean (Siegrist et al.,

1997), maize (Morris et al., 1998), barley (Beber et al., 2000), sunflower (Sauerborn et al.,

2002), tobacco (Perez et al., 2003), amaranthus (Nair et al., 2007), pepper (Baysal et al.,

2005), apple (Bengtsson et al., 2008) and cucumber (Narusaka et al., 1999).

ASM is one of the most potent disease resistance activators used in crops to control

pathogens including viruses (Sindela rova et al., 2002), bacteria (Oh et al., 2004) and fungi

(Achuo et al., 2004). This compound was further developed by Syngenta (Kessmann et al.,

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1996) and introduced in 1996 as a ‘plant activator’ to control wheat powdery mildew in

Germany and Switzerland (Ruess et al., 1996).

It is commercially released in some countries as a plant health promoter of annual

crops under the name of Bion or Actigard (Brisset et al., 2000). Veronesi et al. (2009)

mentioned that foliar spray and soil drenching of ASM and potassium phosphonate reduced

the incidence of broom rape (Orobanche ramose L.) in oilseed rape (Brassica napus L.).

Also, the bio-compatible products Actigard (acibenzolar-S-methyl), disodium hydrogen

phosphate and alum (aluminium potassium sulphate) also suppressed Mungbean Yellow

Mosaic Virus (MYMV) on black gram (Venkatesan et al., 2010). The induction of resistance

with ASM was accompanied by a significant increase in peroxidases and polyphenoloxidases

activities in sugar cane (Ramesh sundar et al., 2006).

Molinari and Baser (2010) stated the use of systemic acquired resistance elicitors like

salicylic acid, methyl salicylic acid, acibenzolar – S- methyl, 2, 6 dichloroisonicotinic acid as

a root dip and soil application to eradicate the egg masses of various root knot nematodes in

solanaceous crops. Development of bacterial blight lesions are reduced in rice plants after

treatment with (1,2,3-benzothiodiazole 7-carbothioicacid S-methyl ester) BTH applications

either as seed treatment or as foliar spray (Karthikeyan and Gnanamanickam, 2011).

Saccharin applied as a root drench was more effective in inducing SAR, against rust

disease in soybean caused by Phakospora pachyrhizi (Srivastava et al., 2011). Also, it is used

to manage the bacterial leaf blight of rice and rice blast disease (Oostendorp et al., 2001).

Resistance inducing chemicals along with macro-micro nutrients would enhance the disease

suppressing mechanism by systemic acquired resistance (Hasan and Samir, 2007).

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Isonicotinic acid and its derivatives have been patented as substances for the

enhancement of plants resistance reactions (Kunz et al., 1988). Nicotinic acid is also known

as a resistance inducing substance in various plants against virus and fungal pathogens

(Dantre et al., 2003; Jaiganesh, 2005).

In cereal crops like barley and rice, biotic and abiotic elicitors have been used to induce

SAR against various plant pathogens and increased the yield characters (Jorgensen et al.,

1998; Du et al., 2000). Foliar application with β-aminobutyric acid and Benzothiadiazole in

sunflower plants offered good protection against downy mildew and increased the yield

characters (Tosi and Zazzerini, 2000). Percival et al. (2009) mentioned that resistance

inducing chemicals sprayed at various growth stages in apple and pear increased the fruit

yield. Potassium dihydrogen phosphate, bion, salicylic acid are the chemical inducers which

increase the yield of chickpea and reduction of Ascochyta blight (Sarwar et al., 2011).

Likewise, several other chemicals are also known to induce resistance in plant against

pathogens. These include Para amino benzoic acid (Grover and Moore, 1962) g-amino n-

butyric acid (Cohen et al., 1999), Indole 3-butyric acid (White, 1979), DL Norvaline

(Shulaev et al., 1995), Polyacrylic (Gianinnazi, 1984), Jasmonic acid and jasmonic methyl

ester (Cohen et al., 1993), Benzimidazole derivatives (Friedrich et al., 1996), DL β – amino

butyric acid (BABA) (Nandeeshkumar et al., 2009), Abscisic acid (Kusajima et al.,2010),

Indole Acetic Acid (Ueno et al., 2011), Potassium phosphonate (Becot et al., 2000) and

Oxalic acid (Sarma et al., 2007).

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Role of salicylic acid in plant defence mechanism and crop yield

Salicylic acid (2-hydroxy benzoic acid; SA) is one of a range of chemicals that induce

systemic resistance (Gorlach et al., 1996). SA is a natural phenolic compound present in

many plants and is an important component in the signal transduction pathway and involved

in local and systemic resistance to pathogens (Delaney et al., 1995). Salicylic acid is a plant-

derived compound and plays an important role in plant defense by the development of SAR

against pathogens (Ryals et al., 1994) and by increasing antioxidant enzymes (Janda et al.,

1999). It was also reported that SA induced plant resistance against pathogens and stimulated

plant growth (Nickell, 1983; Vidhyasekaran, 1990).

Salicylic acid was reported to reduce the mycelial growth and zoospore germination

of P. aphanidermatum (Chen et al., 1999) and was shown to induce resistance to Cucumber

Mosaic Virus (CMV) and increase the yield characters in squash and tobacco (Mayers et al.,

2005; Kone et al., 2009).

Abo-Elyousr et al. (2009) proved that combined application of salicylic acid, bion, T.

hamatum and Paecilomyces lilacinus completely reduced the incidence of root rot disease in

cotton caused by Fusarium spp. and Pythium debaryanum. Similar such results have been

reported in Mulberry (Gupta et al., 2008) and in Chilli (Anand et al., 2009). Foliar

application of salicylic acid significantly reduced the leaf blight disease (Alternaria

alternata) intensity and increased the pod yield (Chitra et al., 2008).

Soaking wheat grains in salicylic acid before sowing significantly reduced the

Bipolaris blight and Fusarium head blight (Hamada and Hashem, 2003). Likewise,

application of potassium phosphite and salicylic acid derivatives at different growth stages of

apple and pear reduced the incidence of Venturia inaequalis (Percival et al., 2009) and

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broccoli seedlings treated with salicylic acid reduced the incidence of club root disease

caused by Plasmodiophora brassicae (Lovelock et al., 2010).

Hammerschmidt and Smith-Becker (1999) mentioned that salicylic acid (SA) affects a

variety of biochemical and molecular events associated with induction of disease resistance.

Spletzer and Enyedi (1999) proved that root feeding of tomato plant with 200 mM SA can (i)

significantly elevate foliar SA levels, (ii) induce pathogenesis-related (PR)-IB gene

expression and (iii) activate SAR that is effective against Alternaria solani.

Growth promoting response was generated in barley seedlings sprayed with salicylic

acid (Pancheva et al., 1996). The foliar application of salicylic acid to soybean also enhanced

the flowering and pod formation (Kumar et al., 1999). Similarly, enhanced germination and

seedling growth were recorded in wheat, when the grains were subjected to pre-sowing seed-

soaking treatment in salicylic acid (Shakirova, 2007). Khodary (2004) observed a significant

increase in growth characteristics, pigment contents and photosynthetic rate in maize, sprayed

with Salicylic acid which enhanced the carbohydrate content also in maize. Eraslan et al.

(2007) revealed that salicylic acid significantly enhanced the overall growth, root dry mass,

sulphur concentration, carotenoids and anthocyanin contents with a concomitant

enhancement of total antioxidant activity in carrot.

In cucumber and tomato, the fruit yield enhanced significantly when the plants were

sprayed with lower concentrations of salicylic acid (Larque-Saavedra and Martin-Mex,

2007). Fariduddin et al. (2003) stated that salicylic acid influences the photosynthetic rate,

carboxylation efficiency, nitrate reductase activity and increased the seed yield in mustard.

The resistance induced by chemical treatment can be very effective (Gorlach et al.,

1996) and may provide commercially useful broad-spectrum plant protection that is stable,

long-lasting and environmentally safe. In some cases, chemical treatment induces expression

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of the same genes and resistance against the same spectrum of pathogens as pathogen-

induced resistance (Mayoral et al., 2010).

Role of Silicon in Plant defense mechanism

Silicon (Si), the second most abundant element of the Earth’s crust, has

been well relied upon by our ancestors, although unknowingly, for protection against fungal

diseases, such as damping-off (Trow 1901) and powdery mildew of cucumber (Belanger et

al., 1995). A review by Epstein (1999), considered the role of silicon on plant disease

management. Silicon is known to reduce infection on various crop plants, partially through

the induction of plant defences (Cherif et al., 1994; Belanger et al., 2003; Walters, 2009).

Also, several studies have confirmed that the severity of powdery mildew on cucumber,

wheat and grape can be reduced through foliar or soil applications of potassium silicate (Lee

et al., 2000; Yildirim et al., 2002; Kanto et al., 2006; Yanar et al., 2011).

Foliar sprays of potassium silicate reduced the incidence and severity of angular leaf

spot of beans caused by Pseudocercospora sp. (Rodrigues et al., 2010) and powdery mildew

disease in tomato caused by Leveillula taurica (Yanar et al., 2011). Liquid potassium silicate

applications have resulted in reduced severities of powdery mildew on strawberry (Kanto et

al., 2006) and grape (Reynolds et al., 1996; Yildirim et al., 2002).

Deren et al. (1994) proved that the increase in rice yield with added silicon was

attributable to a greater number of grains per panicle with brown spot disease being

negatively correlated with Si concentration in the plant tissue. Chang et al. (2002) stated a

significant reduction in bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae

(Ishiyama) due to application of Si. Soybean rust severity at the highest potassium silicate (at

40 g / litre) rate was 70% less than the control treatments (Rodrigues et al., 2009). Similarly,

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rice crop applied with the highest rate of calcium silicate (1000 kg/ha) exhibited the lowest

sheath blight disease severity (Saludares and Alovera, 2009).

The efficacy of silicon nutrients in managing various diseases of crop plants and

increasing the resistance against various pathogens viz., rice brown spot (Junior et al., 2009),

rice leaf blast (Rodrigues et al., 2003), rice neck blast (Datnoff et al., 1991), rice stem rot

(Seebold et al., 2000), Cucumber downy mildew (Cherif et al., 1994), cucumber powdery

mildew (Menzies et al., 1992), Sugarcane ring spot (Matichenchov and Calvert, 2002),

Wheat powdery mildew (Belanger et al., 2003; Remus-Borel et al., 2005), rice sheath blight

(Rodrigues et al., 2001), grape powdery mildew (Bowen et al., 1992), rose black spot

(Gillman et al., 2003), tomato bacterial wilt (Diogo and Wydra, 2007), ring spot in sugarcane

(Ma and Yamaji, 2006), Soybean powdery mildew (Nolla et al., 2006), Potato dry rot (Li et

al., 2009), Coffee root knot nematode (Silva et al., 2010), Phytophthora blight on bell

pepper (French-Monar et al., 2010) and Fusarium root rot of tomato (Huang et al., 2011)

have also been reported.

Datnoff et al. (1991) mentioned a significant reduction in incidence and severity of

brown spot disease in rice plants after calcium silicate application. Several earlier workers

have also reported a significant reduction in rice brown spot incidence and severity by Silicon

application (Nanda and Gangopadhyay, 1984; Deren et al., 1994; Singh and Siddiqui, 2003;

Junior et al., 2009). Silicon increased quality and yield of agricultural crops and has several

beneficial effects on plant growth and crop yields (Ma et al., 2001). Silicon’s importance as a

nutrient has been demonstrated in numerous studies reporting the beneficial effects of silicon

supplementation to agronomic crops, such as rice (Ma and Takahashi, 2002; Gao et al., 2004;

Pereira et al., 2004). It is well documented in rice and sugarcane that fertilization with silicon

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(Si) in soils deficient in soluble Si can reduce disease severity, abiotic stress and increase

yield (Savant et al., 1999; Savant et al., 1997; Datnoff et al., 2001).

An adequate supply of silicon improves the overall plant health by providing

mechanical strength to the entire plant and by inducing resistance to biotic stresses such as

plant diseases and insect pests (Yoshida et al., 1962; Elawad and Green, 1979). Further, it has

been reported that Si increases plant resistance to pests and pathogens (Richmond and

Sussman, 2003) and increased the crop yield (Kaya et al., 2006).

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Materials and methods

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Materials and Methods

General methods

Cleaning of glassware

First of all the glassware were soaked in cleaning solution (100 g of

potassium dichromate was added to 1000 ml of water followed by 500 ml of concentrated

sulphuric acid) for about 12 hr and washed in tap water. Finally they were rinsed in distilled

water, dried and used.

Sterilization

All glassware were sterilized in hot air oven at 1800C for 3hr. Both the solid

and liquid media were sterilized at 15lb pressure for 15 min. in the autoclave.

Chemicals

All the chemicals and reagents used were of analytical reagent (A.R.) quality.

pH

The pH of the medium was adjusted with 0.1 N NaOH or with 0.1 N HCl

Czapek’s Dox Broth (Ainsworth, 1961)

Sucrose : 30 g

Sodium nitrate : 2.0 g

Dipotassium hydrogen phosphate : 1.0 g

Magnesium sulphate : 0.5 g

Potassium chloride : 0.5 g

Ferrous sulphate : 0.01 g

Distilled water : 1000 ml

pH : 6.8 to 7.0

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Potato Dextrose Agar (Ainsworth, 1961)

Peeled potato : 250 g

Dextrose : 20 g

Agar : 15 g

Distilled water : 1000 ml

pH : 6.0 -6.5

Pot culture studies

Separate pot culture studies were conducted to test the efficacy of certain silicon

based nutrients and certain resistance inducing chemicals for assessing their influence on the

incidence of powdery mildew of black gram. The black gram susceptible variety ADT 4

grown in mud pots were used for the study. The crop was maintained in a poly house with

frequent spraying of water to provide adequate moisture and relative humidity to enable

successful infection by the pathogen. The experiments were conducted in a randomized block

design with three replications for each treatment and a suitable control. The fungicide

Mancozeb @ 0.1 per cent was used for comparison and the standard agronomic practices as

recommended by the State Agricultural Department were followed.

Evaluation of silicon based macro-micro nutrients against H.oryzae

Three silicon based nutrients viz., calcium silicate (CS), sodium Silicate (SS) and

potassium silicate (PS) at 0.50, 0.75 and 1.0 per cent conc. were sprayed individually at

disease initiation and repeated once at fifteen days interval.

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Effect of certain resistance inducing chemicals on H.oryzae

Effect of certain resistance inducing chemicals viz., Acetyl Salicylic acid, Benzoic

acid, Nicotinic acid, Propionic acid, Salicylic acid were sprayed at 10, 20 and 50 ppm conc.

individually at disease initiation and repeated once at fifteen days interval.

Disease assessment

In all the studies observations on disease incidence, grain and straw yield were

recorded at the time of harvest. The disease incidence was observed from a randomly selected

set of three hills per pot.

Score description

0 : No symptoms of powdery mildew.

1 : Small scattered powdery mildew specks covering 1 per cent or less leaf area.

3 : Small powdery lesions covering 1-10 per cent of leaf area.

5 : Powdery lesions enlarged covering 11-25 per cent of leaf area.

7 : Powdery lesions coalesce to form big patches covering 26- 50 per cent of leaf

area

9 : Big powdery patches covering 51 per cent or more of leaf area and defoliation

occur.

Pot culture experiment details

Variety : ADT 4

Duration : 65 days

Design : RBD

Replication : 3

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Date of Sowing : 10.01.2012 (first pot culture)

05.03.2012 (Second pot culture)

Location: Department of Plant Pathology, Annamalai University.

Biochemical constituents and enzymes

Method of sampling

Samples of plant materials from each treatment were taken at 0, 7, 14 and 21 days

after spraying both in healthy and diseased plants for estimating the changes in the

biochemical constituents viz., reducing sugars, non-reducing sugars, total sugars, starch, ortho

dihydroxy phenols & total phenol.

Biochemical constituents References

Reducing sugars Nelson, 1944

Total sugars Nelson, 1944

Non reducing sugars Inman, 1965

Starch Summer and Somers, 1949

Statistical analysis

The statistical analysis of the experimental results was performed employing the

computer software package ‘IRRISTAT’, version 90-1, developed by Department of

Statistics, International Rice Research Institute, Philippines and as per the procedure of

Gomez and Gomez (1976).

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Field trail Pod formation stage

First spraying

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Salicylic acid treated plants

Medium Preparation

Powdery mildew – Grade 9

Phytotoxicity symptoms

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Results and discussion

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Results and Discussion

Evaluation of Silicon based nutrients against powdery mildew of black gram

(Pot culture experiment)

The results of pot culture experiments showed that all the silicon based nutrients

reduced the powdery mildew disease incidence over control. Among them, sodium

silicate at one per cent level was the most effective (7.21 %) over the other nutrients

followed by potassium silicate at one per cent in reducing disease incidence (9.52 %) as

compared to 32.40per cent observed in control. Calcium silicate at 0.25 per cent was the

least effective (Table 1).

In general, yield was significantly higher in silicon nutrient treated plots when

compared to test fungicide Mancozeb treated and control plots. Sodium silicate at 1 per

cent level recorded maximum black gram pod yield, followed by sodium silicate @ 0.50

per cent level. There is no significant difference in hundred gram yield among the

treatments. Also, phytotoxicity symptoms observed in potassium and calcium silicate

treated plants.

In the present study the results of pot culture experiments also showed that all

the silicon based nutrients reduced the disease incidence over control (Table 1). The

yield was significantly higher in silicon nutrient treated plots when compared to test

fungicie treated and control plots. Sodium silicate at one per cent level recorded

maximum grain yield and minimum disease incidence.

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Silicon is considered as a beneficial nutrient element in plant biology (Anser, 2009).

It is incontestably an essential requirement for the normal growth of many plants and must be

called as “Quasi essential” (Epstein, 1999). Rice is a best silicon accumulator and its uptake

is about twice that of nitrogen (Savant et al., 1997). Wagner (1940) first reported that Si

application effectively reduced powdery mildew in cucumber.

A review by Epstein (1999), discussed the role of silicon on plant disease control.

Foliar application of soluble Si reduced the powdery mildew severity in cucumber (Lee et al.,

2000), common beans (Rodrigues et al., 2005a) and soybeans (Rodrigues et al., 2005b).

Potassium silicate applications have resulted in reduced severities of powdery mildew on

grape (Yildirim et al., 2002) and strawberry (Kanto et al., 2006). Foliar application of

potassium silicate, as a source of soluble silicon, decreased angular leaf spot severity on

beans (Rodrigues et al., 2005a). Calcium silicate was effective in the reduction of Frog eye

spot, downy mildew and Asian rust in soybean (Nolla et al., 2006) and anthracnose in beans

(Moraes et al., 2009).

A possible effect of foliar application of Si sources on diseases control might be

explained by the establishment of a physical barrier on the host tissue (Bowen et al., 1992).

Silicates act as a bioactive element and are associated with beneficial effects on the

mechanical and physiological properties of plants (Epstein, 2001).

Rodrigues et al. (2004) reported that plant’s defense mechanisms have been triggered

by silicon. Liquid potassium silicate may play a role not only as a physical barrier, but also as

resistance inducer in plants (Ghanmi et al., 2004). Si application might not yield a direct

measurable effect on crop growth, but its positive role on disease suppression may lead to

better plant productivity (Guevel et al., 2007).

32

Thus, increased plant resistance to diseases through Si treatment is associated with

active and/or passive mechanisms (Datnoff et al., 2007).

Several studies have demonstrated that the severity of foliar diseases of various crops

including cereals and pulses can be reduced through foliar or soil applications of potassium

silicate (Rodrigues et al., 2005a; Moraes et al., 2006; Guevel et al., 2007; Buck et al., 2008;

Dallagnol et al., 2009).

Rodrigues et al. (2003) stated that silicon fertilization to rice crop reduced the

incidence of sheath blight. Martinati et al. (2008) proved that potassium silicate treated coffee

plants improved the production, productivity and increased the resistance against coffee rust

caused by Hemileia vastatrix.

Rezende et al. (2009) proved that root and foliar application of potassium silicate can

decrease the intensity of brown spot of rice. Rodrigues et al. (2010) mentioned that bean

plants treated with potassium silicate induced defense mechanism and reduced the severity of

angular leaf spot of beans caused by Pseudocerspora griseola.

The ability of soluble silicon (Si) to reduce the impact of plant diseases has been

sufficiently described in rice and various crops (Belanger et al., 1995; Fawe et al., 2001;

Rodrigues et al., 2003; Kim et al., 2002). Liang et al., (2005) suggested that disease reduction

caused by foliar sprays of potassium silicate was the result of an osmotic effect on spores

germinating at the leaf surface.

It has been reported that potassium fertilizer application can decrease brown spot

severity on rice (Carvalho et al., 2010). The brown spot disease of rice is usually associated

with an imbalance of K (potassium) and N (nitrogen) in rice leaf tissue and K is able to

reduce disease intensity (Baba et al., 1958). The potassium content in potassium silicate

could have also contributed to the enhanced disease suppression. Further, silicon, in the form

33

of silicic acid, would act locally by inducing defense reactions in elicited cells and would also

contribute to systemic resistance by enhancing the production of stress hormones (Fauteux et

al., 2005). Thus, the above reasons could be attributed for the efficacy of foliar sprays of

silicon fertilizers, in reducing the powdery mildew incidence of rice.

Table 2. Evaluation of certain plant activators against powdery mildew of black gram

(Pot culture experiment)

Among the various resistance inducing chemicals, salicylic acid @ 50 ppm was

the most effective (5.30 %) in reducing the powdery mildew incidence followed by

plots sprayed with Acetyl Salicylic acid @ 50 ppm level (7.55 %). It was followed by

Nicotinic acid & Benzoic acid (1000 ppm). Benzoic acid at 10 ppm was least effective.

The test fungicide, Mancozeb was also found to be effective (12.15 %) in reducing the

powdery mildew incidence as against control (34.20 %) (Table 2).

In general, yield was significantly higher in all plant activator treated plots when

compared to test fungicide Mancozeb treated and control plots. Salicylic acid at 50 ppm

level recorded maximum black gram pod yield. There is no significant difference in

hundred gram yield among the treatments. Also, phytotoxicity symptoms observed in all

the chemical inducer treated plants except Salicylic acid.

All the resistance inducing chemicals were found effective in reducing the brown

spot incidence and enhancing the yield when compared to control in pot culture as well

as field studies (Table 8 and Table 12). Among the various resistance inducing

chemicals, salicylic acid (SA) was found as the most effective when compared to other

resistance inducing chemicals.

NAA has been reported to reduce Fusarium wilt of tomato (Corden and Dimond,

1959) and Verticillium wilt of potato (Corsini et al., 1989) through induction of host

34

resistance. Colson et al. (2000) reported that, Bion 50 WG reduced the incidence of

Alternaria microspora on cotton. 2,4-D was found effective against root rot of peanuts

caused by Pythium myriotylum through their effect on root lipids and root lipid

exudation patterns (Hale et al., 1981). Bokshi et al. (2006) indicated that INA increased

chitinase and peroxidase activities and reduced powdery mildew and downy mildew on

leaves of melons. Acibenzolar-S-methyl was effective against blue mould caused by

Peronospora tabacina (Perez et al., 2003; LaMondia, 2009). Foliar application of ASM at

pre flowering period to manage the post harvest rots of rock melon and Hami melons

(Huang et al., 2000) has also been reported. Likewise, the chemical inducer, 2,6-

dichloroisonicotinic acid provided good levels of protection against pear fire blight

(Kessmann et al., 1994) and against apple scab (Ortega et al., 1998). Vechet et al. (2009)

observed that foliar application of salicylic acid increased the resistance in wheat plants

against powdery mildew pathogen. The present findings on the efficacy of resistance

inducing chemicals are also in line with these earlier reports.

Further, resistance inducers when applied exogenously induced the expression of PR

(pathogenesis related) genes, increased the growth characters and also conferred resistance

against various pathogens of viral, bacterial and fungal origin in monocot plants (Morris et

al., 1998; Pasquer et al., 2005; Makandar et al., 2006). Thus, induced resistance may provide

an alternative approach to plant protection especially for problems not satisfactorily

controlled by fungicides (Schoenbeck 1996).

Foliar application of the resistance inducing chemicals at low conc. along with their

non-hazardous nature, simple application procedure, systemic effect and low cost marks this

approach as an effective, feasible and an eco-friendly alternative to conventional chemical

management (Eswaran et al., 2011).

35

Salicylic acid (SA) is a plant-derived compound induced resistance against pathogens

and stimulated plant growth (Nickell, 1983; Vidhyasekaran, 1990). It was also reported that

SA plays an important role in plant defense by the development of SAR against pathogens

(Ryals et al., 1994). SA has been shown to be a signalling molecule involved in both

local defence reactions at infection sites and the induction of systemic resistance

(Durner et al., 1997). SA is a phenolic compound present in many plants and is an

important component in the signal transduction pathway involved in local and systemic

resistance to pathogens (Frey and Carver, 1998).

The findings of Percival et al. (2009) lends support to the present observations on

the use of SA who proved that salicylic acid sprayed at different growth stages in apple and

pear increased the resistance against scab. The use of SA at low conc. is taken up more easily

into crop plants than higher conc. Sometimes, higher conc. of SA treated plants are killed

(Frey and Carver, 1998). In the present study also SA was found very effective at 50 ppm

conc. In this respect, chemicals like salicylic acid may especially be suitably used as inducers

of disease resistance.

Changes in Carbohydrates

Reducing sugars

From the results depicted in table 3, a general reduction was observed in the

quantity of reducing sugars due to treatment with Salicylic acid and Sodium silicate.

Also, decreasing levels of reducing sugar content was observed with increase in time. In

inoculated plants the level of reducing sugar was higher than in control.

36

Non-reducing sugars

Spray with Salicylic acid and Sodium silicate significantly influenced the non-

reducing sugars content when compared to control. In inoculated plants, the non-

reducing sugar content was more in control on 21st day of sampling. The non-reducing

sugars content decreased as the sampling periods increased.

Total sugars

Similar to the trend observed in reducing and non-reducing sugar content, the

treatments with Salicylic acid and Sodium silicate reduced the total sugar content when

compared to control. Maximum total sugar was recorded in control (32.54 mg/g). An

increase in sampling period gradually decreased the total sugar content in all the

treatments (Table 3).

Carbohydrates are the basic building blocks for the synthesis of various defense

chemicals such as phenolics, phytoalexins and lignin. Hence, the quality and quantity of

sugars play an important role in disease resistance (Vidhyasekaran and Kandasamy, 1972;

Vidhyasekaran, 1974). Altering the sugar content of leaves has been shown to be a possible

way to control diseases (Sondeep singh et al., 2009) and interfering with the physiology of

the host could potentially offer an exciting opportunity to control diseases.

Pathogen infection leading to decreased sugar contents has been reported in

sweet corn (Levy and Cohen, 1984). Kalim et al. (2003) reported significant decrease in the

quantity of total soluble sugars in zinc and manganese treated roots of plants inoculated with

Rhizoctonia solani and R. bataticola. The reducing, non and total sugar content were

decreased with increasing conc. of resistance inducing chemicals in H. oryzae infected plants

37

(Vengadesh Kumar, 2005). The exogenous SA application enhanced the carbohydrate content

in maize (Khodary, 2004). Reduction of sugars and accumulation of starch due to the

application of combination of lignite fly ash with potash in blast infected leaves was

reported by Mallika and Ramabadran (1995) and Karpagavalli (1999). These reports

lend support to the present findings.

38

Table 1. Evaluation of Silicon based nutrients against powdery mildew of black gram (Pot culture experiment)

Sl.No. silicon nutrients Disease incidence (%)

Yield (as Kg/ha level)

Hundred black grams weight

(gms)

Phytotoxicity symptoms observed

1. Potassium silicate

0.50 % 13.65 1075 4.2 ---

0.75 % 12.29 1123 4.3 ---

1.0 % 09.52 1216 4.5 observed

2. Calcium silicate 0.50 % 15.47 1081 4.1 ---

0.75 % 13.84 1137 4.2 ---

1.0 % 11.02 1205 4.3 observed

3. Sodium silicate 0.50 % 12.80 1198 4.6 ---

0.75 % 09.92 1306 4.6 ---

1.0 % 07.21 1482 4.8 ---

4. Mancozeb 0.1 % 10.98 1100 4.3 ---

5. Control 32.40 920 4.0

C.D. (p=0.05) 0.243 -- --

39

Table 2. Evaluation of certain plant activators against powdery mildew of black gram (Pot culture experiment)

Sl.No. silicon nutrients Disease incidence

(%)

Yield Hundred black

grams weight

Phytotoxicity

symptoms

observed

1. Acetyl Salicylic

acid

10 ppm 11.79 1222 4.2 ---

20 ppm 09.23 1337 4.3 ---

50 ppm 07.55 1429 4.5 observed

2. Nicotinic acid 10 ppm 14.73 1100 4.3 ---

20 ppm 12.96 1258 4.5 ---

50 ppm 10.08 1330 4.6 observed

3. Salicylic acid 10 ppm 09.83 1285 4.6 ---

20 ppm 07.98 1438 4.8 ---

50 ppm 05.30 1518 5.0 ---

4. Propionic acid 10 ppm 16.72 1092 4.3 observed

20 ppm 14.96 1168 4.4 observed

50 ppm 12.86 1290 4.6 observed

5. Benzoic acid 10 ppm 20.02 1088 4.3 ---

20 ppm 17.95 1143 4.3 ---

50 ppm 15.08 1256 4.4 observed

6. Mancozeb 0.1 % 12.15 1088 4.3 ---

7. Control 34.20 958 4.0 ---

C.D. (p=0.05) 0.371 --- --

40

Table. 3.

Studies on the changes of biochemical parameters in black gram plants due to the treatment with Salicylic acid and potassium silicate application (on 21st day of observation)

Sl.No. silicon nutrients Reducing sugars (mg/g)

Non reducing sugars (mg/g)

Total sugars (mg/g)

1.

Salicylic acid

10 ppm 27.56 04.29 30.79

20 ppm 27.08 04.23 30.47

50 ppm 25.43 04.16 30.08

2.

Sodium silicate

0.25 % 28.05 04.31 31.19

0.50 % 27.24 04.26 30.94

1.0 % 26.72 04.20 30.56

3. Control 28.76 04.38 32.54

41

Summary

42

Summary

The present study was undertaken to investigate the effect of application of chemical

inducers and silicon based nutrient for the successful management of black gram powdery

mildew disease incidence.

Among the various silicon based nutrients Sodium Silicate @ 1 per cent recorded the

minimum disease incidence and maximum yield.

Among the various plant activators Salicylic acid @ 50 ppm recorded the minimum

disease incidence and maximum yield.

The phytotoxicity symptoms observed in potassium silicate, Calcium silicate, Acetyl

salicylic acid, Nicotinic acid and Benzoic acid at various concentrations in black gram

plants.

43

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