Variability within and among populations in the 4-gene system for control of self-incompatibility in Ranunculus polyanthemos

Abstract

Variability at the four S-loci in Ranunculus polyanthemos was studied by means of the 9 S-genes in a tester set of genotypes triply homozygous for the same four of these genes. Individual alleles within each of the four S-loci could be isolated, or the presence of the tester S-alleles could be screened for. Among 29 presumed one-gene samples from three localities on Gotland, only one case of identical genes occurred, indicating several allelic states present for each of the four S-loci. Calculated from the frequencies with which the 9 tester genes were recovered among 375 plants sampled from totally 23 localities in Sweden and the Austrian alps (with the closely related species R. nemorosus) numbers of alleles for the four loci were estimated to 22.3, 17.5, 11.6, and 12.8. An apparent permanence was displayed by the store of alleles, among Swedish localities, between Sweden and Austria, and between R. polyanthemos and R. nemorosus. The store of alleles has become gradually depleted, as R. polyanthemos has moved to the west, over the Swedish mainland. Its permanence and the restricted, not conspicuously uneven sizes of the four S-gene allelic series make gradual improvement of an original multigenic basis seem more likely for the team control than an origin by duplications from an original one-locus basis.