We have developed interspecific hybrids between Brassica oleracea L. and B.campestris L. through ovule culture, which have seed vernalization characteristics, by introducing the seed vernalization character of B.campestris into B.oleracea. Most of the traits in the interspecific hybrids were intermediate between those of the female and the male parents. Chromosome number of the F₁ hybrids after chromosome doubling by colchicine was 38. The most common configuration was 19 bivalents at metaphase in pollen mother cells which contained both of the parental genomes (AACC).
The hybridization was confirmed also in the F₂ hybrids through cytological examination and isozyme analysis. The F₂ amphidiploid hybrids could be vernalized through low temperature treatment at 5°C for 3 weeks at the germination stage. The number of days to flowering was slightly longer than that in the male parent of B.campestris. Proline content in the leaves of the interspecific hybrids was nearly similar to that of the parents, which are heat-tolerant. These hybrids may be heat-tolerant and suitable for cultivation in the tropics.