Genetic studies in brown sarson (Brassica rapa L.)

The present investigation on brown sarson (Brassica rapa L.) was carried out to generate information on genetic variability, degree of interrelationship and combining ability (general and specific), nature and magnitude of gene effects and heterosis for yield of 11 morpho-agronomic and quality traits. The experimental material comprised of a diallel set involving 10 diverse lines excluding reciprocals. Significant variability and GxE interaction was observed for all the traits indicating that the behaviour of parents and crosses was not similar in the random set of environments. The experimental material was evaluated in a randomized complete block design with two replications over two locations namely Regional Rice and Research Station, Khudwani (E1) and Experimental Farm, Division of Plant Breeding & Genetics, Shalimar (E2) of SKUAST-K during rabi 2008-09. The data was recorded on days to 50% flowering, plant height (cm), primary branches plant-1, secondary branches plant-1, number of siliquae on main raceme, number of siliquae plant-1, number of seeds siliqua-1, days to maturity, 1000-seed weight (g), seed yield plant-1 (g), oil content (%) and harvest index (%). Phenotypic and genotypic coefficient of variation was high for seed yield plant-1 followed by primary branches plant-1, secondary branches plant-1, number of seeds siliqua-1 and moderate for secondary branches plant-1 and days to maturity. The expected genetic gain (% of mean) was highest for secondary branches plant-1 followed by seed yield plant-1, number of siliqua plant-1, primary branches plant-1, 1000-seed weight and number of seeds siliqua-1. The lowest genetic gain was observed for days to 50% flowering followed by days to maturity. Seed yield plant-1 exhibited a significant positive genotypic and phenotypic correlation with all the component traits studied. However, it was negatively correlated with maturity days and oil content at both the levels. For yield components significant positive association was revealed between number of siliqua plant-1 and seed yield plant-1, 1000-seed weight and number of seeds siliqua-1, seed yield plant-1 and harvest index both at phenotypic and genotypic levels. The mean values were used for statistical analysis and estimation of genetic parameters following diallel analysis. Analysis of variance revealed significant differences among the parents and their crosses for all the traits in the individual environment and the data pooled over environments. The variance due to GCA and SCA was significant for all the traits which showed that both were important in the inheritance of the traits. Significant interaction between combining ability effects and environments were observed for all the traits. The estimates of dominance variance were higher in magnitude than their corresponding additive genetic variance in the individual as well as pooled analysis indicating preponderance of non-additive gene action. Estimates of average degree of dominance revealed preponderance of overdominance for all the traits. None of the parents was found to be a good general combiner simultaneously for all traits. However, CR-1617 was identified as a good general combiner for most of the traits viz., days to 50 per cent flowering, plant height (cm), secondary branches plant-1, number of siliquae on main raceme, number of siliquae plant-1, days to maturity, 1000-seed weight and seed yield plant-1, CR-2871 was the best general combiner for oil content and CR-2630 for harvest index. Overall ranking of genotypes revealed that genotypes CR-1617, CR-2638, CR-2677, CR-1607, CR-1480, KOS-1 and KS-101 could be useful sources of elite alleles based on their general combining effects. The most promising crosses that revealed highly positive and significant SCA effects for yield and yield attributing traits were CR-1485 x CR-1607, CR-1485 x CR-2871, CR-1480 x CR-2677, CR-2871 x KOS-1, CR-2638 x KOS-1, CR-2677 x KOS-1 and CR-2677 x KS-101 (E1, E2 and pooled analysis). The component analysis indicated preponderance of non-additive gene effects in the inheritance of all the traits. Net dominance effect over all loci in heterozygotes ( ) was significant and positive for all traits indicating unidirectional dominance, which was also confirmed from the value of / that indicated asymmetrical gene distribution. The value of KD/KR was more than one indicating presence of excess of dominant genes in parents, which was also verified by / value in almost all the cases. The graphical analysis indicated overdominance in case of 1000-seed weight and oil content (E1, E2 and pooled analysis) whereas, partial to complete dominance was observed for rest of the traits. Significant value of t2 alongwith significant deviation of regression coefficient from unity, indicated presence of non-allelic interactions, for secondary branches plant-1 and number of siliquae on main raceme, low to moderate estimates of heritability (narrow sense) were recorded. Significant and desirable mid and better parent heterosis was observed for most of the traits. The maximum heterosis for seed yield plant-1 was registered in CR-1485 x CR-1607, CR-1677 x KS-101, CR-1485 x CR-2871, CR-2677 x KS-101 and CR-1607 x CR-2677 (mid and better parent estimates). Higher magnitude of mid and better parent heterosis in the favourable direction for seed yield and component traits suggested the possibility of yield enhancement in brown sarson through the exploitation of heterosis breeding provided an economically feasible method is available for production of commercial hybrids