Relationship of molecular and phenotypic divergence with hybrid performance in Indian mustard (Brassica juncea)

Predicting hybrid performance from the parental generation could largely enhance the efficiency of hybrid breeding programmes. To determine the relationship of parental distances estimated from phenotypic traits and SSR markers with F1 performance, average heterosis and heterobeltiosis in 44 indigenous and exotic genotypes of Indian mustard [Brassica juncea (L.) Czern. and Coss.], were studied. Jaccard’s genetic distances (JD) and Manhattan genetic distances (MD) were taken as criteria to classify the genotypic pairs into four diversity groups, viz. high, intermediate high, intermediate low and low. Seventy crosses representing the four diversity groups each for JD and MD were evaluated. Placement of higher number of significantly better hybrids was in extreme diversity groups created using JD, while, it was higher in intermediate diversity groups generated through MD. Low regression values were observed between JD among genotypic pairs and mean performance (R2 = 0.02), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.15). Similarly, low regression values were observed between MD among genotypic pairs and mean performance (R2 = 0.033), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.009). The slope of linear regression curve, placement of hybrids on the plot and low regression values in all the cases revealed that there is no significant association between genetic distance and hybrid performance. Therefore, desirable genetic diversity, in form of heterotic pools, needs to be identified from indigenous and exotic germplasm for expression of heterosis.