LAUSR

In order to clarify the origin of the evolutionary transition from self-incompatibility (SI) to self-compatibility (SC), genetic relationships among local accessions of wild common buckwheat, Fagopyrum esculentum subsp. ancestrale, showing SI, and its sister species Fagopyrum homotropicum, which shows SC with homostyly, were investigated based on nucleotide variation in nuclear EST sequences. Nucleotide diversity in these species was comparable irrespective of the mating system. Phylogenetic analyses revealed that wild common buckwheat was divided into northern and southern groups, and F. homotropicum was more closely related to the southern group of wild common buckwheat. Furthermore, F. homotropicum showed polyphyly with two distinct groups, indicating independent origins of the two different lineages. This is the first report of the multiple origins of homostylous self-compatible lineages from a single heterostylous self-incompatible species, which has been previously suggested with less concrete evidence in the same species complex. Differentiation between these groups was also evident from the degree of crossability to common buckwheat. Phylogenetic network pattern, composite-likelihood estimates of migration, and the similar level of nucleotide diversity between wild common buckwheat and the major group of F. homotropicum suggest historical gene flow between them. Introgression from wild common buckwheat as well as the advantage of SC in spreading to a novel habitat may have contributed to the northward expansion of the distribution range of F. homotropicum.