Interspecific Incompatibility Between Brassica napus and B. oleracea
Brassica napus is an amphidiploid species which may be resynthesized by intercrossing the parental species, B. campestris and B. oleracea. While the two parent species are self-incompatible, each possessing a single-locus sporophytic self-incompatibility system, B. napus is usually self-compatible. Test crosses between cultivars of each of these three species showed that pollen from B. oleracea usually failed to penetrate the stigmatic surface of B. napus pistils although all other combinations of interspecific crosses were compatible with respect to pollen-tube penetration. Three out of four synthetic B. napus lines, obtained by embryo culture following interspecific pollinations of B. campestris with B. oleracea, were also incompatible when pollinated with B. oleracea pollen although the parental lines used were reciprocally cross-compatible. However, the fourth synthetic was reciprocally compatible with B. oleracea. The interspecific incompatibility could be overcome by bud pollination or by treatment with cycloheximide as is the case for intra-specific incompatibility in Brassica species.