Resynthesizing Brassica napus from interspecific hybridization between Brassica rapa and B-oleracea through ovary culture

Using three varieties of Brassica rapa, cv. Hauarad (accession 708), cv. Maoshan-3 (714) and cv. Youbai (715), as the maternal plants and one variety of B. oleracea cv. Jingfeng-1 (6012) as the paternal plant, crosses were made to produce interspecific hybrids through ovary culture techniques. A better response of seed formation was observed when ovaries were cultured in vitro at 9-12 days after pollination on the basal MS and B5 media supplemented with 6-benzylaminopurine (BA) and naphthylacetic acid (NAA). The best response was observed for cross 714 x 6012 with the rate of seeds per ovary reaching 43.0%. Seeds for cross 715 x 6012 showed the best germination response (66.7%) on the regeneration medium (MS + 1.0 mg l(-1) BA + 0.05 mg l(-1) NAA). In all three cross combinations, good response in terms of root number and length of plants was observed on the root induction medium (MS + 1.0 mg l(-1) BA + 0. 1 mg l(-1) NAA). A better response was observed for the regenerated plants cultured for 14 days than for 7 days. The ovary-derived plants with well-developed root system were hardened for 8 days and their survival rate reached over 80%. Cytological studies showed that the chromosome number of all plants tested was 19 (the sum of both parents), indicating that these regenerated plants were all true hybrids of B. rapa (n = 10) x B. oleracea (n = 9). The regenerated plants were doubled with colchicine treatment, and the best response in the crosses 708 x 6012, 714 x 6012 and 715 x 6012 was observed when treated with 170 mg l(-1) colchicine for up to 30 h and their doubling frequency reached 52, 56 and 62%, respectively.