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Volume 7, Issue 4, August Issue - 2019, Pages:376-381


Authors: P. Roopa Sowjanya, E. Gangappa, S. Ramesh
Abstract: Testing of inbred lines for general combining ability (gca) enables plant breeders to discard undesirable ones and identify those that are desirable for the production of superior hybrids. In this context, 16 inbred lines were selected on the basis of grain yield and were evaluated for their gca related to grain yield plant-1 and its attributing traits. The analysis of variance revealed significant differences among the inbred lines for their per se performance as well as their gca. Similarly the hybrids differed significantly for per se performance and their specific combining ability (SCA) effects for all the traits. Five of the 16 inbred lines were identified as good general combiners for grain yield plant-1. Non-significant correlation between per se performance and gca effects suggested that per se performance of inbred lines is not a good indicator of their gca effects for any of the traits. However, significant positive and fairly high magnitude of correlation between per se performance of hybrids and sum of parental gca effects indicated good predictability of hybrids per se performance based on their parental gca effects for all the traits investigated.
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Full Text: 1 Introduction Single cross hybrids are the major cultivar types used for commercial production of maize in most parts of the world. Hybrids have played a vital role in increasing the area and productivity of maize. Superior hybrids are produced if the parents involved have good general combining ability (gca), which is the relative ability of a genotype to transmit its genes with additive effects to its progeny. The concept of gca (Sprague &Tatum, 1942) is a widely accepted criteria for assessing the inbreds for their use as parents in the development of heterotic hybrids. Testing of inbreds for their gca effects enables plant breeders to discard most of the undesirable inbreds and allows greater expenditure of resources on most promising ones and identifies those that are desirable for the production of superior hybrids (Bernardo, 2010; Ali et al., 2011; Ai-Zhi & Zheng, 2012; Fasahat et al., 2016; Hosana et al., 2016 ). Apart from providing an objective criterion for choosing parents, gca also provides useful clues about mode of action of genes controlling economically important traits. Another utility of gca of the parents is their predictive power of hybrid per se performance in the absence of significant hybrid specific combining ability (sca) effects. Under these premises, an investigation was undertaken to assess the gca of inbred lines and hybrids of maize 2 Materials and Methods 2.1 Basic material Based on prior evaluation of 16 inbred lines of maize were selected based on high grain yield, and they constituted the basic genetic material. 2.2 Development and field evaluation of experimental material These 16 inbreds were crossed following half diallel mating design (Hayman, 1954) to develop 120 single cross hybrids (SCH) during summer 2015 at the experimental plots of the Department of Genetics and Plant Breeding (GPB), University of Agricultural Sciences (UAS), Gandhi Krishi Vignana Kendra (GKVK), Bengaluru. The resultant 120 SCH, their parents and two checks viz., Hema and Nithyashree constituted the experimental material and were evaluated following simple lattice design. Each entry was sown in two-rows of 3 m length with a spacing of 0.6 m × 0.3 m. All the recommended package of practices was followed to raise a healthy crop. 2.3 Sampling of plants and data collection Data were recorded on five randomly selected plants in both the replications, on each hybrid, parent and checks for grain yield plant-1 and its attributing traits. 2.4 Statistical analysis Replication wise mean data of hybrids, parents and checks was used for statistical analysis. Data of F1 hybrids were subjected to combining ability analysis following diallel model (Hayman, 1954; Griffing, 1956). The gca effects of 16 lines were estimated and their statistical significance was examined using ‘t’test.  2.5 Relationship of gca effects of inbred lines with their per se performance Relationship between per se performance of 16 inbred lines and their gca effects were determined by estimating Spearman’s Rank Correlation Coefficient for all the traits. Higher magnitude of positive significant and non-significant correlation indicates good and poor predictive power of per se performance, respectively. 2.6 Relationship of hybrid per se performance with sum of parental gca effects Pearson’s Correlation Coefficients between hybrids per se performance and sum of gca effects of their parents were estimated for all traits (Schrag et al., 2009). Significant correlation with fairly high coefficients of correlation and determination was interpreted as high predictability of hybrid per se performance based on their sum of parental gca effects. 3 Results and Discussion 3.1 Analysis of variance (ANOVA) ANOVA indicated significant differences among single cross hybrids for all the traits (Table 1). Significant mean squares due to inbreds and hybrids suggested substantial variability for gca effects of inbreds and sca effects of their crosses for all the traits. Significant variances among the crosses could be attributed to greater diversity between inbreds for the traits considered. The mean squares attributable to inbreds and crosses for all the traits indicated greater contribution of the inbreds towards total variation among the hybrids (Kanagarasu et al., 2010). 3.2 General combining ability of inbred lines The practical phase of hybrid maize breeding is identification of elite inbred lines with high gca for use as parents for developing hybrids that are superior to existing ones (El-Hosary, 2014). Identification of such elite inbred lines is the major strategy adopted by most commercial plant breeders to maximize genetic gain per unit time and resources. This assumption is based on the reports that gca is controlled by additive effect genes which control the inheritance of phenotypes that are fixable (Ai-Zhi & Zheng, 2012). In the present study, the inbred lines differed widely for their gca effects for all the Six quantitative traits. The differences in gca effects of the inbreds are attributable to differences in frequencies of genes that are transmitted to the progeny with the additive effects (Falconer & Mackay, 1996). The differences in gene frequencies among the inbreds suggest their significant genotypic differences, thus justifying their selection for the present study. Different inbred lines were desirable general combiners in both direction and magnitude for different traits (Table 2). Thus, no single line was a desirable combiner for all the seven traits. For instance, inbreds such as MQPM 43, 18816, MAI 386, 18701 and 754 were desirable general combiners for only grain yield plant-1, plant height, number of kernel rows-1, ear length and ASI, respectively (Table 2). However, inbred lines MAI 386 and MQPM 43 were good general combiners for four traits, namely ASI, ear length, Kernel row-1 and grain yield plant-1. Thus the inbred lines MAI 315, MAI 157 and M2 need greater attention and need to be evaluated on a large scale to confirm their superiority for gca effects. It should however be noted that the estimates of gca effects of 16 inbred lines are relative to and are dependent on particular set of parents included in the experiment (Fasahat et al., 2016). 3.3 Relationship of gca effects of inbred lines with their per se performance Significant positive but low magnitude of correlation between per se performance of the inbreds and their gca effects          for ASI, ear length, ear width, kernels rows-1, Kernel rows ear-1 (Figure 1-6), suggested that per se performance of the lines is not a good indicator of their gca effects for any of the traits. The poor correlation between per se performance and gca effects of inbred line could be attributable to different sets of genes controlling   per se performance and gca effects for target traits (Turner, 1953; Ai-Zhi & Zhang, 2012). Significance of mean squares attributable to gca and sca (Table 1) provide evidence for the involvement of both additive genetic variance and dominance genetic variance for the expression of grain yield plant-1 and its attributing traits. 3.4 Relationship of hybrid per se performance with sum of parental gca effects Relatively high magnitude of correlation between sum of the parental gca effects with hybrid per se performance for all the traits (Figure 7-12), suggested that parental gca effects retained fairly higher predictability of hybrid per se performance. It helps to predict hybrids performance based on their parental gca which is attributable to additive effect genes (Falconer & Mackay, 1996). Prediction of hybrid heterosis based on parental gca effects would save substantial resources as it enables the evaluation of only a few hybrids that are predicted to be most promising ones. The utility of parental gca effects for predicting hybrid per se performance has also been reported by Schrag et al. (2009) and Sowmya & Gangappa (2018). Conclusion From this study it is evident that the correlation between per se performance of hybrids and sum of parental gca effects will help in predicting  the hybrids per se performance based on their parental gca effects for all the traits investigated, Hence,  gca of parents can be used as a predictive tool for developing  hybrids with superior per se, which in turn helps in reducing the  use of input resources and enhances the breeding efficiency. Acknowledgement The senior author thankfully acknowledges the financial support from University Grant Commission (UGC) in the form of Rajiv Gandhi National Fellowship (RGNF) for pursuing Ph.D. programme.  Conflict of Interest: Nil
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