S-HAPLOTYPE POLYMORPHISM IN BRASSICA OLERACEA

Abstract

Self-incompatibility (SI) promotes outcrossing in Brassica species and has been exploited for producing Fl hybrids in cole crops. The SI locus (S-locus) is very polymorphic and cross-compatibility between plants depends on the allelic forms (S-haplotypes) of genes at the S-locus. Among these genes, SLG (S-Locus Glycoprotein gene) is specifically expressed in the stigma. Two classes (class I and class II) of SLG genes have been described and antibodies allowing a specific identification of class I or class II SLG are available. In this paper, we report the polymorphism in Brassica oleracea cultivars (cauliflower, broccoli, romanesco, cabbage, kale and wild forms of the Normandy coast) as assessed by using an isoelectric focusing and immunostaining combined analysis. Plants from an S-allele collection obtained from Dr D. Ockendon were also introduced in the analysis to allow the identification of S-haplotypes according to his nomenclature. Using the two class-specific-SLG antibodies, approximately 80 different immunostaining patterns were identified out of the 950 plants analysed. However, we were unable to find specific immunostaining patterns for about 10% of the analysed plants. Among these plants, we identified 9 S-haplotypes by crossing experiments with lines of known S-haplotype. We also observed that three S-haplotypes (S2, S29, S63) gave variable immunostaining patterns, where SLG bands were either clearly detectable, faintly detectable or not present. This indicates that, in these particular S-haplotypes, the amount of SLG is highly dependent on the genetic background of the plants. All but one of the S-' haplotypes described in the wild forms were also found in cultivated forms. The three class II haplotypes (i.e., S2, S5, S15) were detected in wild Brassica but only S15 was common to all cultivated as well as wild Brassica plants. Moreover, S15 was the most frequent S-haplotype detected in the species.