Development of self-incompatible Brassica napus: (III) B. napus genotype effects on S-allele expression

Use of self‐incompatibility (SI) as a pollination control method for Brassica napus hybrid production requires the development of a sufficient number of S‐alleles that are expressed consistently in a range of B. napus lines. Self‐incompatibility (SI) alleles have been transferred from Brassica oleracea and Brassica rapa into B. napus var. oleifera. An understanding of expression of these alleles in B. napus is essential for their commercial use. Four SI B. napus doubled haploids containing the B. oleracea S‐alleles S2, S5, S13 and S24 were crossed to three B. napus cultivars to measure the B. napus genetic background effect on S‐allele expression. A line x tester analysis indicated that the largest source of variation in the expression rate of SI was the S‐allele itself. The B. napus genotypes tested contained modifier gene(s), some that enhanced SI expression and others that inhibited SI expression. The B. napus Canadian cultivar ‘Westar’ generally had a negative effect on SI expression while the European cultivar ‘Topas’ had a positive effect on the B. oleracea S‐allele expression. The B. oleracea S‐allele S24 was very similar in expression to the B. rapa allele W1. The application of these results for the use of B. oleracea S‐alleles for hybrid production in B. napus is discussed.