Analysis of Heterosis, Combining Ability and Genetic Diversity in Tuber Mustard (Brassica juncea var. tumida Tsen & Lee) Inbred Lines Based on SSR Markers and Combining Ability Estimates

Fifteen inbred lines of tuber mustard were used to determine their genetic diversity by using simple sequence repeat (SSR) markers and seven inbred lines (male) and eight sterile male inbred lines (female) were crossed to obtain 56 hybrids. Heterosis and combining ability were analyzed among these hybrids. We detected 80 pairs of SSR primers amplifying 637 bands among the parents, with an average of 8.0 and ranging from 3 to 13. The genetic distances between the male lines and the male sterile lines ranged from 0.25 to 0.40, with an average of 0.33. Fifteen accessions were classified into two clusters based on genetic distance. The combining ability analysis showed that five significant positive relative effects and 24 significant positive relative effects were found in general combining ability (GCA) and specific combining ability (SCA) analyses, respectively. Thirty-six hybrids showed significant positive effects in high-parent heterosis, indicating that heterosis in stem yield among parents was evident in tuber mustard. Because heterosis of stem yield in tuber mustard among the parents was associated with GCA and SCA, attention should be paid to both GCA and SCA in breeding for tuber yield heterosis. The correlation coefficients of genetic distance between stem yield, high-parent heterosis and SCA were all small and not significant. Further study is necessary to determine whether or not genetic distance could be used to predict heterosis and SCA in stem yield of tuber mustard.