Heterotic patterns in rapeseed （Brassica napus L.） using exotic germplasm for Chinese semi-winter hybrid breeding

Chinese semi-winter rapeseed, genetically differing from winter and spring rapeseed, has been consid- ered to possess strong potential as parent in winter and spring rapeseed hybrid breeding programs. However, no de- tailed researches have been documented whether winter and spring rapeseed lines have potential for Chinese semi- winter rapeseed hybrid breeding. The objectives of this study are to estimate the potential of winter and spring rapeseed for semi-winter rapeseed hybrid breeding, and to investigate the association of general combining ability （GCA） with adaptation of parental lines by combining with the data in our previous studies. Four winter and four spring male sterile lines were crossed with 14 Chinese semi-winter rapeseed lines to develop 112 hybrids, which were evaluated together with their parents for seed yield under three environments in China. The exotic parental lines were not adapted to local environment as demonstrated by late flowering, low seed weight and poor seed yield per se. However, the hybrids, especially derived from winter rapeseed exhibited strong heterosis for seed yield, indicating that winter rapeseed germplasm has a great potential for rapeseed hybrid breeding in China. Our data suggested a strong association of GCA with their adaptation ability of parental lines, since high to middle cor- relations were found for local parental lines and low correlations for exotic parental lines under spring, winter and semi-winter eco-growth environments. The hybrid breeding program using exotic germplasm in rapeseed was discussed.