INBRED LINES WITH DOMINANT INCOMPATIBILITY ALLELES FOR USE AS PARENTS OF F1-HYBRID BRUSSELS-SPROUTS

To improve the chances of obtaining highly self-incompatible inbred lines for use as parents of F1 hybrid Brussels sprouts [Brassica oleracea var. gemmifera] and to extend the range of mutually cross-compatible combinations available, new inbred lines are being produced from plants selected for the presence of dominant S-alleles. The material comprises 42 different inbred families representing 15 cultivars and contains 12 dominant S-alleles of uncommon occurrence in Brussels sprouts. Data on S-allele interactions in the material are presented. Tests showed that while many of the parent plants containing dominant S-alleles were highly self-incompatible, a few had only weak self-incompatibility. Although the chances of obtaining strongly self-incompatible inbreds may be increased by using material with dominant S-alleles, it remains necessary to test and select for strong self-incompatibility during the breeding program. Production of such inbred lines requires the application of 2 independent selection procedures, one for agronomic type and one for S-allele constitution. Only a small proportion of the plants of a parent cultivar are acceptable on both counts. Large populations of the cultivar and large numbers of selections are necessary; this in turn involves much expensive S-allele screening. To alleviate this problem, a wide-based panmix containing only dominant S-alleles is being produced. It is hoped that from this it will be possible to extract inbred lines which carry only dominant S-alleles, so avoiding the need to screen each parent plant for its S-allele content.