66 F1 hybrids, produced by 3 double low self-incompatible lines and 22 varieties with a North Carolina Ⅱ (NCⅡ) crossing design, were tested for their heterosis in Wuhan, China during two growing seasons from 1999- 2001. The results showed that significant differences were found between F1s and their parents for yield per plant and seed oil content. Mid-parent heterosis of these two characters ranged from 5.50%-64.11% and from 1.55% -7.44% respectively. Heterosis for seed yield per plant was greater than that of seed oil content. For yield components, heterosis of total number of siliques per plant was the highest, followed by seed number per silique and 1 000 seeds weight. Significant genotype-by-year interaction was found for seed yield per plant. Results from correlation and combining ability analysis indicated that parental effects on its F1 hybrid depended on characters, seed yield per plant was affected by both additive and non-additive effects, and seed oil content was affected mainly by additive effect. When designing hybrid programme, parents might be selected by GCAs and variances of SCAs of parents for the characters affected by both additive and non-additive effects, and by the sum of GCAs of female and male parents for the characters mainly affected by additive effects.
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