RELATIONSHIP BETWEEN HETEROSIS AND GENETIC-DISTANCE BASED ON RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM MARKERS IN OILSEED RAPE (BRASSICA-NAPUS L)

Significant heterosis for seed yield in oilseed rape (Brassica napus L .) has created interest in the development of hybrid cultivars. The ob jective of this study was to determine the value of restriction fragme nt length polymorphism (RFLP) markers in predicting hybrid performance . The hybrids and parents of two sets of dialler crosses were evaluate d at three environments for seed yield and other agronomic traits. The parents of the first diallel were seven oilseed rape cultivars and th e parents of the second diallel were seven unselected S-6 lines derive d from the cultivars. Genetic distances (GD) between the parents cross ed in the diallels were estimated by RFLP data from 43 DNA clones. Bot h general combining ability (GCA) and GD estimates were significantly (P < 0.05) correlated with hybrid seed yield in both diallels, althoug h GCA was more greatly correlated than GD. Genetic distance was signif icantly correlated with heterosis for seed yield only in the inbred di allel whereas GCA was significantly correlated with heterosis only in the cultivar diallel. Midparent yield was significantly correlated onl y with heterosis for the cultivar dialler. A multiple linear regressio n model that included both the GD and GCA of the parents was more grea tly correlated with hybrid seed yield than any variable alone. The GCA values were significantly correlated with hybrid plant height, and se ed oil and protein concentration in both diallels whereas GD was signi ficantly correlated only with hybrid plant height. These results sugge st that GD estimates alone do not identify high yielding hybrid combin ations with the consistency to be useful in breeding programs.