S-allele diversity in a natural population of Physalis crassifolia (Solanaceae) (ground cherry) assessed by RT-PCR.

Allelic diversity at the self-incompatibility (S-) locus in the ground cherry, Physalis crassifolia (Solanaceae), was surveyed in a natural population occurring in Deep Canyon, CA, using a molecular assay to determine the genotype of individual plants. A total of 28 different S-alleles were identified and sequenced from a sample of 22 plants. All plants examined were heterozygous, as expected under gametophytic self-incompatibility (GSI). The estimated number of alleles in this population is 43-44, comparable to allelic diversity reported for other species, as determined by the standard diallel crossing method. Allele frequencies in the sample deviated from the expectation of equal frequency under GSI; it is suggested that this deviation may result from sampling of related individuals. Molecular analysis of genotypes within single pollen donor families indicates that, for all alleles examined, segregation is consistent with predictions for single-locus GSI. The implications of a reliable and efficient molecular assay for determining the S-genotype of plants are discussed.