CONSERVATION OF S-LOCUS FOR SELF-INCOMPATIBILITY IN BRASSICA-NAPUS (L) AND BRASSICA-OLERACEA (L)

Self-incompatibility (SI) in Brassica is a sporophytic system, genetic ally determined by alleles at the S-locus, which prevents self-fertili zation and encourages outbreeding. This system occurs naturally in dip loid Brassica species but is introduced into amphidiploid Brassica spe cies by interspecific breeding, so that in both cases there is a poten tial for yield increase due to heterosis and the combination of desira ble characteristics from both parental lines. Using a polymerase chain reaction (PCR) based analysis specific for the alleles of the SLG (S- locus glycoprotein gene) located on the S-locus, we genetically mapped the S-locus of B. oleracea for SI using a F-2 population from a cross between a rapid-cycling B. oleracea line (CrGC-85) and a cabbage line (86-16-5). The linkage map contained both RFLP (restriction fragment length polymorphism) and RAPD (random amplified polymorphic DNA) marke rs. Similarly, the S-loci were mapped in B. napus using two different crosses (91-SN-5263 x 87-DHS-002; 90-DHW-1855-4 x 87-DHS-002) where th e common male parent was self-compatible, while the S-alleles introgre ssed in the two different SI female parents had not been characterized . The linkage group with the S-locus in B. oleracea showed remarkable homology to the corresponding linkage group in B. napus except that in the latter there was an additional locus present, which might have be en introgressed from B. rapa. The S-allele in the rapid-cycling Brassi ca was identified as the S-29 allele, the S-allele of the cabbage was the S-5 allele. These same alleles were present in our two B. napus SI lines, but there was evidence that it might not be the active or majo r SI allele that caused self-incompatibility in these two B. napus cro sses.