Heterosis of Double Low Self-incompatibility Line in Oilseed Rape (Brassica napus L.)

F 1 hybrids, produced by three double low self-incompatible lines and 22 varieties with a North Carolina II (NCII) mating design, were tested for their heterosis in Wuhan in two growing seasons from 1999 to 2001. The results showed that significant differences were observed between F 1 and their parents for yield per plant and seed oil content. Mid-parent heterosis for the two characters was ranged from 5.50% to 64.11% and from -1.55% to 7.44%, respectively. Heterosis of seed yield per plant was higher than that of seed oil content. For yielding components, heterosis of total number of siliques per plant was the highest, followed by seeds per silique and 1 000-seed weight. Significant genotype-by-year interaction was found for seed yield per plant. Results from combining ability analysis showed that seed yield per plant was affected by both additive and non-additive effects, while seed oil content was affected mainly by additive effect. In hybrid breeding, parental materials might be selected by the total GCAs of female and male parents for characters mainly affected by additive effect, and by GCAs and variances of SCAs of parents for characters affected by both additive and non-additive effects, respectively.