The S-allele collection of Brassica oleracea

Over the past 30 years the S-allele collection of Brassica oleracea has been improved by detecting and eliminating duplicate alleles, and by cleaning up lines where the desired allele was contaminated by a second S-allele. These problems often involve recessive S-alleles, which may give a weak self-incompatibility reaction when homozygous, or no reaction at all when heterozygous with a dominant S-allele. Eventually the 47 numbered lines originally received were reduced to 36. From extensive S-allele surveys of most of the cultivated and wild forms of the species, a further 14 S-alleles have been added to the collection, making a total of 50. A complete list of all S-allele numbers is given, showing the current status of each, details of duplication and contamination, and their distribution. Early work on the collection was done using seed set, but later on pollen tube growth counts were used, because these gave quicker and more accurate results. More recently molecular methods based on DNA analysis have been developed, and now that DNA sequence data is available for most S-alleles, this may become the preferred method of identification. The S-allele collection has been widely used both for breeding purposes and for the study of self-incompatibility, and has become an international standard. The Genetic Resources Unit at Wellesbourne has a vital role in conserving authenticated samples of the collection, and providing material for distribution.