Inheritance of seeds per silique in Brassica napus L. using joint segregation analysis

Seeds per silique (SS) is one of three important components of yield in rapeseed. Genetic control of this trait was primarily studied in 2006 in the cross of ‘HZ396’ × ‘Y106’, in which ‘Y106’ is a higher-SS line and ‘HZ396’ is a lower-SS one. The frequency distribution of the F2 generation deviated from a normal distribution and appeared to have a multi-modal pattern, indicating the influence of major genes mixed with polygenes. To test this hypothesis and uncover the genetic basis of SS in diverse genotypes, we further used the joint segregation analysis (JSA) of six populations (P1, P2, F1, F2, B1 and B2) in the crosses of ‘HZ396’ × ‘Y106’ and ‘HZ165’ × ‘Y106’ and four populations (P1, P2, F1, F2) in the cross of ‘HZ168’ × ‘Y106’ in 2008. The JSA revealed that SS was best described by the E-0 genetic model, a case of two additive-dominace-epistasis major genes as well as additive-dominace-epistasis polygenes. We observed considerable genetic diversity in all genotypes by evaluating the first- and second-order genetic parameters based on the JSA method. Variance analysis of genotype × year interaction revealed the steady genetic effects of the two major genes within different years. The additive effects of the two major genes ranged from −3.71 to −1.49 in the three crosses. Heritability of the major genes varied from 39% to 84% in diverse generations (B1, B2 and F2), which was much larger than that of the polygenes. These findings will facilitate breeding strategies for SS improvement as well as efforts to map the major genes.