The number, dominance relationships and frequencies of self-incompatibility alleles in a natural population of Sinapis arvensis L. In South Wales

Abstract

The incompatibility genotypes of a further 25 plants from the South Wales population of Sinapis arvensis studied by Ford and Kay (1985) have been determined, and an additional 21 S-alleles have been found. This brings the overall number of plants analysed from the population to 35, and the total number of S-alleles found also to 35. It is estimated that there are 52 S-alleles in the population. Dominance interactions between S-alleles have been established in a total of 42 different heterozygotes (pooling data obtained during the present study with that of Ford and Kay (loc. cit.)). Co-dominance of alleles in both pollen and stigma occurred in 18 (42·8 per cent), dominance of one allele in the pollen occurred in 21 (50 per cent), dominance of one allele in the stigma occurred in two (4·8 per cent), and dominance of one allele in both pollen and stigma occurred in one (2·4 per cent). There is a minimum of three levels in the pollen dominance hierarchy, and two in the stigma dominance hierarchy; dominance interactions between S-alleles in the stigma may be non-linear. There is some indication that pollen dominant alleles tend to be found in lower frequencies than pollen recessive alleles. Preliminary data show that at least some S-alleles in S. arvensis have a very wide geographical distribution. © 1989, The Genetical Society of Great Britain.