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 objective of this study was to determine the value of restriction fragment length polymorphism (RFLP) markers in predicting hybrid performance. The hybrids and parents of two sets of dialler crosses were evaluated at three environments for seed yield and other agronomic traits. The parents of the first diallel were seven oilseed rape cultivars and the parents of the second diallel were seven unselected S-6 lines derived from the cultivars. Genetic distances (GD) between the parents crossed in the diallels were estimated by RFLP data from 43 DNA clones. Both general combining ability (GCA) and GD estimates were significantly (P < 0.05) correlated with hybrid seed yield in both diallels, although GCA was more greatly correlated than GD. Genetic distance was significantly correlated with heterosis for seed yield only in the inbred diallel whereas GCA was significantly correlated with heterosis only in the cultivar diallel. Midparent yield was significantly correlated only with heterosis for the cultivar dialler. A multiple linear regression model that included both the GD and GCA of the parents was more greatly correlated with hybrid seed yield than any variable alone. The GCA values were significantly correlated with hybrid plant height, and seed oil and protein concentration in both diallels whereas GD was significantly correlated only with hybrid plant height. These results suggest that GD estimates alone do not identify high yielding hybrid combinations with the consistency to be useful in breeding programs.