Late leaf spot (LLS) caused by Phaeoisariopsis personata is the major foliar disease that reduces the pod yield and severely affects the fodder and seed quality in groundnut. Molecular markers linked with LLS can improve the process of identification of resistant genotypes. In the present study, a LLS susceptible genotype (TMV 2) and the LLS resistant genotype (COG 0437) were crossed and their F 2 population was used for marker analysis. The phenotypic mean data on F 2:3 progenies were used as phenotype. Parents were surveyed with 77 SSR (Simple Sequence Repeat) primers to identify polymorphic markers. Among SSR markers, nine primers were found polymorphic between the parents TMV 2 and COG 0437. These markers were utilized for bulked segregant analysis (BSA). Among the polymorphic SSR markers, three primers viz., PM 375 162 , pPGPseq5D5 220 and PM 384 100 were able to distinguish the resistant and susceptible bulks and individuals for LLS. In single marker analysis, the markers PM 375, PM 384, pPGPseq5D5, PM 137, PM 3, PMc 588 and Ah 4-26 were linked with LLS severity score. The phenotypic variation explained by these markers ranged from 32 to 59 %. The markers identified through BSA were also confirmed with single marker analysis. While validating the three primers over a set of resistant and susceptible genotypes, the primer PM 384 100 allele had association with resistance. Hence PM 384 could be utilized in the marker assisted breeding programme over a wide range of genetic background.
Three varieties, CO 4, Morden and TNHSF 239 (a pre-release culture) and two hybrids, TCSH 1 and KBSH 44, were selected for this study. Simple correlation coefficients were estimated among characters for individual varieties and hybrids. Two traits, seed yield and 100-seed weight, are important selection indices for oil yield improvement in both varieties and hybrids. Head weight can be considered as a selection index for improvement of seed and oil yield in hybrids only. Likewise, oil content is an important selection index for oil yield improvement in varieties. It can also be inferred that the results obtained from the association analysis of pooled data for varieties and hybrids will give ambiguous results and have a negative impact on the yield improvement program. Thus it is desirable to compute separate association analyses for each variety and hybrid to identify effective selection indices for the improvement of sunflower.
The correlation coefficients among nine yield and yield attributing characters with their path effects towards kernel yield were investigated in F3 generation for three crosses of groundnut during Kharif-2009. From association studies, kernel yield was significant and positively correlated with number of pods per plant, pod yield per plant, shelling percentage and hundred kernel weight for all the crosses. The path analysis indicated that among the nine traits studied, pod yield per plant exerted maximum positive direct effect on kernel yield per plant for all the three crosses. When both direct and indirect positive contributions were considered, number of pods per plant and pod yield per plant influenced kernel yield per plant. Thus, on the basis of correlations and direct and indirect effects, number of pods per plant, pod yield per plant, hundred kernel weight and shelling percentage were proved to be the outstanding characters influencing kernel yield in groundnut and need to be given importance in selection to achieve higher kernel yield.
Three way hybrids numbering sixty involving six parents were tested in randomized block design with three replications. The mean data on number of mature pods per plant were analyzed as per a triallel analysis model. The character showed predominantly epistatic genetic variance. The magnitude of additive x dominance types of epistasis was maximum followed by dominance x dominance and additive gene effects respectively. The dominance and additive x additive type of gene effects were negative. The combining ability analysis revealed that ALR 2 was a good grand parent as well as third parent and GG 2 good third parent in three-way crosses. The cross combination (JL 24% Co 2) x GG 2 gave the highest three line specific effect. Whereas, the other combinations of the same three parents (JL. 24 x GG2) x Co 2 and (GG 2 x Co 2) x JL 24 exhibited negative estimates. As the epistatic gene action predominated, attempting multiple crosses or intermating of early generation segregants besides postponing the selection to later generation may yield fruitful results for the improvement of pod number in groundnut.
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