The inheritance of quantitative traits in Brassica napus ssp rapifera (swedes): Augmented triple test cross analyses of production characters

Two F-2 triple test crosses, augmented with F(3)s, produced from crosses between different inbred lines of swedes (Brassica napus ssp. rapifera L.) were assessed in field trials at Dundee in 1988 and 1989, respectively. This paper reports the analyses of resistance to powdery mildew, neck length, growth cracks, sugar content and hardness; analyses of yield have been published previously. Additive genetical variation was found for all traits while non-additive variation was less important, the highest degree of dominance being 0.44 for hardness. There was evidence of additive x dominance and dominance x dominance epistasis for mildew and additive x additive epistasis for neck length and hardness. Significant, consistent reciprocal differences were found and these were particularly large for neck length and growth cracks. Sugar determination was carried out on the basic generations of the second cross, the parental lines of which showed large differences in concentration of glucose, fructose and sucrose. Directional dominance was found for high glucose but not for fructose or sucrose. The implications of these results for swede breeding are discussed and it is proposed that inbred cultivars would be a more practical option than F-1 hybrids.