Relationships between genetic distance, combining ability and heterosis in rapeseed (Brassica napus L.)

Present study was conducted to evaluate the relationship between parental genetic distances, combining ability and heterosis in rapeseed (Brassica napus L.). Nine elite inbreds widely used in Chinese rapeseed breeding programs, were crossed in a diallel design to develop 36 hybrids and evaluated together with their parents across four environments. Genetic distances among lines were measured from 11 morphological traits, and SSR and SRAP molecular markers. Results showed that genetic distance evaluated by total molecular markers (GDtotal) had no correlation with heterosis. In order to make a better prediction, significant markers and favoring markers were selected from the total molecular markers, and results revealed that genetic distance measured by favoring markers (GDfavor) significantly and positively correlated with number of seeds per silique, thousand seed weight, seed yield per plant and seed yield per plot for high-check heterosis (HCK) and sum of parental general combining ability (GCA(f+m)). The selected favoring markers could be used for the further study on prediction of heterosis for yield and yield related traits. The magnitudes of correlation coefficients of morphological distances with mid-parent heterosis, high-parent heterosis and HCK for yield and other traits were mostly not significant. Interestingly, more higher levels of correlations were found between GCA(f+m) and heterosis, which indicated that using the information of GCA(f+m) to predict heterosis appeared an important method in rapeseed. Three out yielding crosses, 8D129 × 8E001 (HCK, 23.56%), 8C189 × 8C272 (23.31%), and 8C343 × 8D129 (20.08%), were identified as ideal hybrids evaluated across four environments and may be promoted for adoption and commercialization in China.