Deletion Mutations of the Self-incompatibility (S) Locus Induced by Gamma Irradiation in a Wild Diploid Species of Sweet Potato, Ipomoea trifida

Gamma irradiation was used to induce mutations affecting self-incompatibility (SI) in diploid Ipomoea trifida. Plants (S-1 homozygote) with developing flower buds were exposed with gamma rays of 10 and 20 Gy. Mature pollen from the irradiated plants was used for crosses with S-3 and S-10 homozygotes. By pollination test and Southern blot analysis of the M-1 progenies, we screened 2 mutant plants carrying a deletion of the S locus derived from irradiated pollen, designated Delta S-1. In both mutant alleles, the deleted region was found to exceed a genetic distance of 12 cM around the S locus. Progeny test of both mutant plants showed that neither female nor male gametes carrying the Delta S-1 allele were fertile probably due to the lethal effect of the chromosomal deletion spanning the S locus.