Population variability in wild turnip (Brassica rapa var. oleifera) for interspecific hybridisation with herbicide-resistant rape (Brassica napus) pollen

As a basis for risk assessment for the release of transgenic rape (Brassica napus) plants, this study investigates the potential for hybrid formation between a non-transgenic herbicide-resistant rape (AACC; 2n = 4x = 38) as the pollen parent and six New Zealand populations of wild turnip (Brassica rapa var. oleifera) (AA; 2n = 2x = 20) as the maternal parent. Following hand pollination, 41% of pollinated stigma developed into siliques with seeds. The frequency of successful pollination varied significantly between wild turnip populations and was higher on flowers from lower racemes than upper racemes. The wild turnip populations also differed in the number of seeds per silique. In all populations, fewer seeds developed in siliques from the upper raceme compared with the lower raceme. Over 99% of successfully germinated progeny were chlorsulfuron-resistant, with the seed germinating as chlorsulfuron-sensitive seedlings (0.7%) presumed to be matromorphic seed. Flow cytometry established that the chlorsulfuron-resistant seedlings were triploids, thereby confirming their hybrid status. The frequency of dormant seeds did not differ between wild turnip populations, although the upper racemes produced 6-fold more dormant seed than the lower racemes.