SHORT NON-REFEREED PAPER

PHENOTYPIC CORRELATIONS OF LEAF-SHEDDING AND FIBRE CONTENT WITH YIELD AND QUALITY

TRAITS IN SUGARCANE GENOTYPES

NXUMALO PD1 AND ZHOU MM1,2,3

1South African Sugarcane Research Institute, P/Bag X02, Mount Edgecombe 4300, South Africa 2University of the Free State, Plant Sciences Department, Breeding Division, PO Box 399,

Bloemfontein 9300, South Africa 3University of KwaZulu-Natal, P/Bag X01, Scottsville 3290, South Africa

Phumla.Nxumalo@sugar.org.za Marvellous.Zhou@sugar.org.za

Introduction

Sugarcane is an economically important commercial crop in South Africa and plays a role as an agricultural and economic resource. However, infestations of sugarcane by the stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae) (eldana) reduce yield and quality of sugarcane (Goebel and Way, 2003; Rutherford, 2015). The damage caused by the tunnelling and feeding of eldana inside the stalks is further exacerbated by the colonisation of borings by Fusarium, a fungus which causes red discolouration in the internodal tissues (Rutherford, 2015). Direct and/or indirect sugar losses caused by eldana in South Africa are currently estimated at more than R1 billion per annum (Rutherford, 2015). The objectives of sugarcane breeding programmes include high yield, high quality and eldana resistance (Tyagi et al., 2012). However, interrelationships between yield, quality and resistance traits influence the success of a variety (Ali et al., 2018; Shitahun et al., 2018). Therefore, knowledge of trait association is used in breeding and developing strategies for indirect selection particularly for traits that are difficult to measure (Jamoza et al., 2014; Mishasha et al., 2018 Ali et al., 2018). Several studies have determined interrelationships among cane yield and quality characters (Sandhu and Saini, 1997; Jamoza et al., 2014; Shitahun et al., 2018). However, limited knowledge is available for associations between cane yield and quality traits with pest and disease resistance traits. Therefore, the objective of this study was to determine phenotypic correlations among leaf-shedding, fibre content (traits associated with eldana resistance), yield and quality traits in the South African Sugarcane Research Institute (SASRI) sugarcane breeding programme, and evaluate implications on eldana resistance breeding.

Materials and Methods

Data were collected from a Stage II TSL16 Single line trial planted at Empangeni Research Station (103 masl; 28°45’S, 31°54’E) in 2016. This agro-ecological region represents areas with high rainfall, high temperature, and deep and rich soils that contribute to the production of high yielding varieties. A total of 164 families were selected from seedlings in Stage I. Each family was made up of several genotypes planted as 8 m single row plots. Families were replicated three times while genotypes were not replicated due to large numbers at the early stage of testing and screening. Data were collected in 2017. At crop maturity, 12 stalks from each genotype (single line) were examined and scored for leaf-shedding, and assessed for eldana damage. Leaf-shedding was scored from 0 to 3, with 0 representing clinging leaves, 1 representing slight leaf-shedding, 2 representing intermediate leaf-shedding and 3 representing high leaf-shedding. After scoring for leaf-shedding, sugarcane trash was detached and the stalks were examined for eldana entry and exit holes and the number of damaged stalks was recorded for each genotype. The 12 stalks

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were then bundled together and sent to the SASRI laboratory, where they were analysed Brix % cane (Brix), BrixDM % cane (BrixDM), Estimated recoverable crystal % cane (ERC), Pol % cane (Pol), Purity % (Purity), Fibre % cane (Fibre) and Dry matter % cane (DM) using standard methods (Shoonees-Muir et al., 2009). The Pearson and Spearman rank correlation analyses were done on individual genotypes per family using Proc CORR of the statistical analysis system (SAS institute, 2012).

Results and Discussion Similar trends were observed between Pearson and Spearman correlations. Results obtained from the Pearson correlation analyses are presented in the current study (Table 1). Pearson correlation measures the strength of a linear relationship between two variables, but does not determine cause and effect (Hauke and Kossowski, 2011). Leaf-shedding, which is the natural detachment of leaves from the point of attachment showed significant (P<0.05) negative correlations with stalk numbers (r=-0.05) and non-significant (P>0.05) positive correlations with diameter (r=0.06). However, significant (P<0.05) positive correlations were observed with stalk height (r=0.21), TSH (r=0.12), TCH (r=0.11) suggesting that an increase in leaf-shedding will have no negative impact on these yield related traits within this population. Leaf-shedding had significant (P<0.05) and positive correlation with ERC (r=0.04), Brix% cane (r=0.06) and Pol (r=0.05). This indicates that selecting for increased leaf-shedding will not negatively impact quality traits. Non-significant (P>0.05), negative and positive correlations were observed for BrixDM % cane and Purity, respectively. Leaf-shedding showed significant (P<0.05) negative correlations with PBS (r=-0.08), suggesting that selecting for increased leaf-shedding would decrease PBS, thus decreasing damage caused by eldana. The results obtained suggest that selection of genotypes with increased levels of leaf-shedding will not negatively impact yield and quality traits, and may indirectly increase yield and quality while reducing eldana damage. Positive phenotypic correlations between leaf-shedding, yield and quality traits suggest that leaf-shedding could be added as an additional selection trait without negatively compromising yield and quality traits.

Table 1. Pearson phenotypic correlations among sugarcane quality traits measured on genotypes selected within 164 families.

Above diagonal: Pearson, Below diagonal: Spearman, PBS - % bored stalks, LS – Leaf-shedding, Diam – Diameter, TCH – Tons cane per hectare, ERC – Estimated recovery crystal, TSH – Tons sugar per hectare, DM – Dry matter, Brixdm – Brix dry % matter, Brix cane – Brix % cane, Pol – Polarisation, ns – non-significant, *significant at P<0.05, ***significant at P<0.01, ***significant at P<0.001

Trait PBS LS Fibre Stalks Diam Height TCH ERC TSHS DM Brixcane Brixdm Purity% POL

PBS -0.08*** -0.20*** -0.02ns 0.14*** -0.11*** -0.004ns -0.36*** -0.16*** -0.42*** -0.30*** -0.04*** -0.38*** -0.35***

LS -0.07*** 0.09*** -0.05*** 0.06ns 0.21*** 0.11*** 0.04* 0.12*** 0.13*** -0.06*** -0.03ns 0.02ns 0.05***

Fibre -0.22*** 0.09*** 0.13*** -0.35*** 0.16*** -0.06*** -0.02ns -0.06*** 0.64*** -0.28*** -0.83*** 0.38*** -0.09***

Stalks -0.03ns -0.06*** 0.122*** -0.36*** -0.02ns 0.41*** -0.10ns 0.33*** 0.002ns -0.14*** -0.17*** -0.02ns -0.11***

Diam 0.14*** 0.06*** -0.33*** -0.35*** 0.05*** 0.29*** -0.01ns -0.25*** -0.24*** 0.08*** 0.28*** -0.16*** 0.01ns

Height -0.12*** 0.19*** 0.16*** -0.01ns 0.05*** 0.53*** -0.02ns 0.47*** 0.10*** -0.04*** -0.13*** 0.04*** -0.02ns

TCH -0.0009ns 0.10*** -0.06*** 0.41*** 0.29*** 0.52*** -0.03* 0.88*** -0.06*** -0.01ns 0.04* -0.04*** -0.03ns

ERC -0.31*** 0.03* -0.02ns -0.09*** -0.002ns -0.05ns -0.05*** 0.42*** 0.73*** 0.93*** 0.55*** 0.85*** 0.99***

TSH -0.14*** 0.12*** -0.06*** 0.33*** 0.24*** 0.46*** 0.87*** 0.39*** 0.27*** 0.40*** 0.28*** 0.34*** 0.42***

DM -0.40*** 0.12*** 0.64*** 0.02ns -0.24*** 0.09*** -0.08*** 0.69*** 0.23*** 0.56*** -0.11*** 0.81*** 0.69***

Brixcane -0.24*** 0.05*** -0.28*** -0.13*** 0.08*** -0.04*** -0.02ns 0.92*** 0.38*** 0.51*** 0.76*** 0.60*** 0.96***

Brixdm -0.01ns -0.02ns -0.82*** -0.15*** 0.27*** -0.13*** 0.03*** 0.53*** 0.27*** -0.13*** 0.74*** 0.10*** 0.61***

Purity% -0.34*** -0.003ns 0.40*** 0.004ns -0.19*** 0.04*** -0.06*** 0.80*** 0.30*** 0.79*** 0.53*** 0.04*** 0.79***

POL -0.29*** 0.04* -0.09*** -0.11*** 0.02ns -0.02ns -0.04*** 0.99*** 0.39*** 0.65*** 0.96*** 0.59*** 0.73***

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Fibre content is part of the cane that is insoluble in water, and is made up of lignin, cellulose and hemicellulose. Fibre showed significant (P<0.05) negative correlations with PBS (r=-0.20) indicating that an increase in fibre would reduce eldana damage. Fibre was significantly (P<0.05) and negatively correlated with sucrose related traits viz Brix% cane (r=-0.28), Brix DM% cane (r=-0.83) and Pol% cane (r=-0.09), and was non-significantly (P>0.05) and negatively correlated with ERC (r=-0.02). Previous research reported negative association between fibre and eldana damage (Mahlanza et al., 2014). However, fibre content is negatively associated with sucrose content (Singh et al., 2013). This suggests the need to determine optimum fibre content that minimises effect on sucrose content for commercial sugarcane breeding. Although, significant (P<0.05) positive correlations were observed with stalk numbers (r=0.32) and stalk height (r=0.16), fibre was significantly (P<0.05) and negatively correlated with stalk diameter (r=-0.35), TCH (r=-0.06) and TSH (r=-0.06) suggesting a decrease in stalk diameter, sugar yield and overall tonnage with the selection of increased fibre. A study by Sajjad and Khan (2009) reported on fibre as a good contributor for sugarcane yield characters and that of Singh et al. (2013) reported the selection of moderate rind hardness (regulated by fibre % cane) for good yield as well as sugar recovery. This indicates the need to determine optimum fibre content that reduces effect on cane yield for variety improvement. Fibre was significantly (P<0.05) and positively correlated with Purity (r=0.38), possibly coincidental increase in fibre and Purity with crop maturity.

Conclusions The negative and significant correlation between leaf-shedding and PBS suggests that leaf-shedding is an important selection trait for reducing eldana damage. Furthermore, the positive and significant association among yield (TCH, TSH and stalk height) and quality traits (Brix DM % cane, Brix % cane, Purity, Pol, ERC) indicates that leaf-shedding as an additional selection trait has positive benefits on other commercial traits. Negative correlations between fibre and PBS, sucrose and yield traits suggest that while higher fibre reduces eldana damage, selecting for fibre may unintentionally lower sucrose content and overall sugar yield.

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