S-alleles and mating system in natural populations of Capsella grandiflora (Brassicaceae) and its congeneric relatives

Abstract

Population-level estimates and studies on geographical distribution of S-alleles (SRK-alleles) are missing for most self-incompatible species. We screened natural populations of the self-incompatible diploid Capsella grandiflora for SRK-alleles and identified 63 alleles altogether across its whole distribution area. The native range in Greece had 61 alleles whereas in the introduced range in northern Italy only 20 alleles could be detected. Allozyme studies confirmed outbreeding in natural populations of C. grandiflora in general, but observed heterozygosity levels were low in some loci. Moreover, lower multi-locus outcrossing rates were recorded for the mainland Greece populations. In contrast to the SRK-allele profiles, we found no differences in allozyme profiles between native and introduced ranges. We detected five SRK-alleles in the diploid self-compatible C. orientalis while four SRK-alleles were discovered in the allotetraploid C. bursa-pastoris. Capsella bursa-pastoris shares SRK-alleles with both of its parent species, C. grandiflora and C. orientalis.