Abstract
Gametophytic self-incompatibility (SI), an important character for breeding seedless cultivars of Citrus, is known in pummelo, mandarin, and many hybrid cultivars with pummelo in their pedigrees. Only a little is known about the allelic variation in the self-incompatibility gene (S), S allele frequencies, and the genotypes of self-incompatible and semi-self-compatible cultivars. In this study, pollination of ‘Banpeiyu’ S1 seedlings with ‘Banpeiyu’ and pollination between the S1 seedlings were performed to determine homozygous S1 seedlings for the S gene. Seventy-eight Citrus accessions, including 55 pummelo accessions, were pollinated with each of two homozygous S1 seedlings (S1S1 and S2S2). Pollen tube arrest in the style base of their pollinated pistils indicated that 23 accessions, including ‘Banpeiyu’, have an S1 allele each and 16 accessions, including ‘Banpeiyu’, have an S2 allele each. Frequency of accessions with S1 allele was 29.9% (23 of 77 accessions examined) and S1 allele frequency was 16.4% (23 of 140 alleles excluding Sf allele). Frequency of accessions with S2 allele was 21.3% (16 of 75 accessions examined) and S2 allele frequency was 11.6% (16 of 138 alleles excluding Sf allele). Pummelo accessions collected from Kagoshima Prefecture had S1 alleles with two and half times higher frequency (56.3%) than that in all accessions examined. Of the 79 accessions, six accessions (‘Banpeiyu’, ‘Iriki Buntan’, ‘Kaopang’, Nagashima Buntan No. 6, Nagashima Buntan No. 7, and ‘Soyu’) were S1S2 genotypes. The Citrus cultivars, whose S genotypes have been fully determined in this study, were ‘Banpeiyu’ (S1S2), ‘Iriki Buntan’ (S1S2), ‘Kaopang’ (S1S2), ‘Soyu’ (S1S2), ‘Kinukawa’ (SfS2), and ‘Kawano Natsudaidai’ (SfS2).
