The analysis of variance (Table 1a) for combining ability revealed that the mean sum of squares due to lines were significant for days to flowering, days to 50% flowering, days to maturity, plant height, secondary branches per plant and length of main shoot. The mean sum of squares due to testers was significant for plant height, total number of siliquae per plant and length of siliqua. Interaction effect for lines and testers was significant for all the traits. The variation due to parents vs. crosses was highly significant for all the characters except days to flowering and days to 50% flowering, suggesting the presence of heterosis for these characters in the crosses. Highly significant differences were recorded among the treatments for all the traits Similar finding were earlier reported by
Arifullah et al. (2013);
Synrem et al., (2015); Meena et al., (2015) and
Chauhan et al., (2017). Similarly, highly significant variance due to crosses for all the traits was also observed by
Synrem et al., (2014) and
Meena et al., (2015) disclosing sufficient amount of genetic variability in the hybrids.
The estimates of SCA variances were higher than GCA variance (Table 1b) for all the characters studied indicating that dominance variance was more than the additive variance. The ratio of variance due to general and specific combining ability was less than unity for all the traits highlighting preponderance effect of non-additive gene action. So, for the improvement of these traits, bi-parental mating followed by recurrent selection would be rewarding to get desirable recombinants. The present finding confirmed the study reported by
Thakral et al., (2000);
Singh et al., (2005); Gami and Chauhan (2013) and
Chauhan et al., (2017).
The estimates of GCA effects of lines and testers are presented in Table 2 and it revealed that the parents namely, PM 24, PM 25, PM 30, Pusa Agrani and JD-6 among lines and Pusa Bold among the testers exhibited significantly positive GCA effects for seed yield per plant. So, additive gene action or additive × additive type of interaction effects mainly controlled these parents. Similarly, such additive type gene effect was also found in parents PM 25, PM 30, Pusa Agrani, JD-6, Pusa Bold and Kranti which exhibited significant GCA effects for siliquae/plant; PM 21, PM 24, Pusa Agrani, Sanjukta Asech and Sarama for siliqua length; PM 24, PM 25, Pusa Agrani, JD-6, Sanjukta Asech and Pusa Bold for seeds/siliqua; PM 21, PM 22, JD-6, Sanjukta Asech, Seeta and Sarama for 1000- seed weight; PM 22, PM 24, Pusa Agrani and Pusa Bold for days to maturity; PM 22, PM 24, PM 30, Pusa Agrani, JD-6, Sarama, Pusa Bold and Kranti for plant height; PM 25, PM 30, Pusa Agrani, JD-6 and Pusa Bold for primary and secondary branches/plant. The parent PM 25 had highest GCA effects among the lines for seed yield/plant followed by JD-6. Similarly, among the testers, only Pusa Bold had significant positive GCA effects for seed yield/plant. These parents can be utilized in further breeding program. Combining all traits the parents PM 24, PM 25, PM 30, Pusa Agrani, JD-6 and Pusa Bold appeared to be consistently superior for seed yield and important yield components consistently showing significantly positive SCA effects and thus the parents were mainly controlled by additive gene effect. All these parents can be considered as good general combiner for seed yield and important yield attributing traits like number of siliquae/plant, number of seeds/siliqua, number of primary branches/plant, plant height, days to maturity and so plants with higher yield coupled with more number of siliquae and early maturing lines would hopefully can be developed from segregating generations with fixable effect in nature.
Specific combining ability effect is a very important estimate for determining the potentiality of cross combination. In this study, out of 35 hybrids none of the crosses showed significant SCA effect for all the traits (Table 3). Similar results were observed by
Patel et al., (2015) and
Synrem et al., (2015) also in their study. For days to flowering and maturity, earliness is a desirable criteria and so negative SCA effect was desirable. Similarly, for dwarf plant height is desirable in mustard and thus the hybrids which exhibits significantly negative SCA effects for these traits are of paramount importance in breeding program. For days to flowering 16 crosses showed highly significant but negative SCA effects. Similar effects were observed 18 crosses for days to 50% flowering, 11 for days to maturity and 16 crosses for plant height. This indicates that the earliness in days to flowering, days to 50% flowering and days to maturity and reduction in plant height are possible to achieve and these negative trend are to be incorporated in high yielding background. Similar results of negative SCA effect for days to maturity and plant height were earlier reported by
Yadava et al., (2012) and
Meena et al., (2015). Significant and positive SCA effects were recorded for seed yield in 11 hybrids, 1000-seed weight in 19 hybrids, siliquae/plant in 13 hybrids, length of siliqua and seed/siliqua in 15 hybrids each, primary branches/plant in 10 hybrids and secondary branches/plant in 15 hybrids. All these crosses can be considered as good specific combiners.
The five best cross combinations having significantly positive SCA effects (Table 3 and Table 4) namely, JD-6 × Pusa Bold, PM 30 × Seeta, PM 25 × Pusa Bold, PM 24 × Kranti and PM 22 × Sarama showed that good specific combinations involve parents of high × high, high × low, low × low general combining ability effects. The crosses also showed significantly positive SCA effect for most of the traits (Table 3). Parents with high GCA effect are always favorable in a self-pollinated crop like mustard as characters with additive gene effect can be fixed at an early segregating generation
(Singh et al., 1993). From these results it is clear that best cross combination are not always obtained from parents having high × high or high × low general combiners. In majority of the crosses expressing high SCA effects were found to have both or one of the parents as good general combiner for the trait under study. Hence, the ideal cross combination to be exploited is one which shows high magnitude of SCA in addition to GCA in both or at least in one of the parents. However the cross combinations where both parents are involved with non-additive gene effect can be useful for heterosis breeding or in such cross combination delayed selection can be practiced to get desirable recombinant type with homozygous effect
(Singh et al., 1991).
The five best performing parents as good general combiners, best performing hybrids along with their heterosis (%) over mid parent as well as better parent and SCA effects for seed yield per plant is presented in Table 5. The estimates of SCA effects showed that five hybrids
viz. JD-6 × Pusa Bold, PM 30 × Seeta, PM 25 × Pusa Bold, PM 24 × Kranti and PM 22 × Sarama exhibited significant and positive SCA effects for seed yield/plant. The performance of hybrids with compare to heterosis over mid parent (MP) and better parent (BP) for seed yield/plant revealed that out of total 35 crosses, five crosses also exhibited highly positive significant heterosis (Table 5). High amount of heterobeltiosis observed under the present study agreed with earlier reported by
Vagela et al., (2011) and
Patel et al., (2015). Yadava et al., (2012) who reported 54.38% heterobeltiosis in hybrid PM 25 × RGN 145 with highly significant SCA effects.
Yadava et al., (1974) reported up to 239% heterosis over better parent and
Verma et al., (2011) reported 24.36 to 80.97% heterosis in 15 crosses for seed yield per plant in mustard. Combining estimates of GCA, SCA and heterosis, five cross combinations namely JD-6 × Pusa Bold, PM 30 × Seeta, PM 25 × Pusa Bold, PM 24 × Kranti and PM 22 × Sarama appeared superior for developing desirable lines as all these crosses were controlled by additive gene effect and also showed high heterosis for seed yield and several traits.
