Distribution of S-alleles and breeding structure of Cape broccoli (Brassica oleracea var.‘italica’)

Abstract

182 plants representing 7 cultivars of Cape broccoli were tested for their S-alleles using the standard Brassica S-allele collection. In all but 12 plants both S-alleles were identified. A total of 20 different S-alleles were found, 9 of which occurred in the autumn types but not in the spring, 5 of which occurred in the spring types and not the autumn, and 6 of which were common to both. Most of the S-alleles detected in Cape broccoli were also found in Brussels sprouts or kales, but of the three which were not, two were confined to Cape broccoli while the third occurred only in Cape broccoli and Savoy cabbage. By far the commonest S-allele in Cape broccoli was S2, with an overall frequency of 35%. Three S-alleles were found (S14, S25 & S45) which were completely recessive in the stigma in certain combinations. The general pattern of distribution of S-alleles in Cape broccoli, with highly unequal frequencies, was similar to that in Brussels sprouts. The results indicate a high level of outcrossing in Cape broccoli which has implications for the breeding of this crop.