自家不和合性における自他認識に直接的に関わるS遺伝子の同定を試みた。複数のS遺伝子座を単離して解析したところ、S遺伝子座周辺領域長は、S遺伝子の優劣性に従って優性のものほど長くなっていた。また、自家和合性突然変異体の解析から、S候補遺伝子のうち、AB2(♂側)とSEA(♀側)が有力な候補であることが示された。サツマイモ栽培種(I.batatas)も、I.trifidaの自家不和合性と同一の分子基盤に基づく不和合陛を有しており、その解析の結果、I.trifidaのS_3遺伝子型は、I.batatasにも保存されていることが示された。Wild type sweet potato (Ipomoea trifida) has sporophytic self-incompatibility (SSI) system, but this system is not based on the SPII/SCR and SRK system, which is observed in Brassica. To identify S genes of Ipomoea SSI system, S-locus genomic regions from several S-haplotypes, including self-compatible (Sc) mutant, were isolated and analyzed. According to the shotgun sequencing of S-locus genomic regions from four S-haplotypes, the length of the S-locus genomic region was parallel to the dominant-recessive hierarchy of S-genes ; longer in dominants, shorter in recessives. In the Sc mutant line, all S-candidate genes ; AB2 for male, and SE2 and SEA for female ; were located in the Sc-S-locus, however, AB2 and SEA genes were duplicated, and two SEA genes indicated ectopic expression in the male reproductive organs. It is possible to consider that this ectopic expression of SEA genes make Sc line as self-compatible. S-candidate gene analyses of wild type (I.trifida) and cultivated (I.batatas) indicated that S_3 haplotype ofLtrifzda is conserved in the I.batatas. This result indicates that the self/cross-incompatibility in cultivated sweet potato is based on the same molecular mechanism as in the self-incompatibility of I.trifida.