A molecular approach to the identification of S-alleles in Brassica oleracea

A molecular technique for the identification of S-alleles involved in self-incompatibility has been used to analyse the S-allele reference collection of Brassica oleracea. The reference collection contains nearly 50 different lines each with a different S-allele present in the homozygous state. The technique consists of amplifying by the polymerase chain reaction (PCR) sequences belonging to the S multigene sequence family using a single pair of conserved primers. PCR products are then analysed further by digestion with six restriction enzymes followed by gel electrophoresis of the digestion products. A simple method of estimating the band sizes of the digestion products is described. The S-locus-related sequences can be distinguished from S-locus glycoprotein and S-receptor kinase genes by the restriction patterns. Furthermore, with any one restriction enzyme, several alleles showed the same restriction pattern. Alleles could therefore be grouped together. With two exceptions, each member of the S-allele reference collection showed a unique set of restriction patterns. Investigation of the exceptions using pollen tube growth tests showed that these accessions represented duplications within the collection. This technique therefore provides a simple and useful method for identifying different S-alleles.