Advance in S allele determination, S allele frequencies and S-genotyping in citrus

Gametophytic self-incompatibility (SI) is known in pummelo, mandarin and cultivars with pummelo in theirpedigrees. Despite the importance of SI for citrus cultivation and breeding, little is known about the SIgenotypes of citrus cultivars. In this study, homozygous S₁ seedlings for the S gene were produced throughbud self-pollination of five monoembryonic SI cultivars, i.e., 'Banpeiyu' and 'Hirado Buntan' pummelos(Citrus grandis), clementine (Citrus clementina) and 'Ellendale' mandarins and 'Hassaku' (Citrus hassaku). The homozygosity of S₁ seedlings for S gene was determined by pollen tube penetration in the stylar base 8 days after pollination with the parent, and homozygous genotypes were determined similarly by pollinationsbetween the homozygous S₁ seedlings. The determined homozygous S₁ seedlings, whose S genotypes wereS₁S₁, S₂S₂, S₃S₃ and so on, were pollinated to about 100 SI (S_nS_n') or SC (SfSf or SfS_n) cultivars and accessions. The cultivars or accessions arresting pollen tubes in their stylar base were determined to have the sameallele as that of the pollinated homozygous seedling. Cultivars whose S genotypes were determined were'Banpeiyu' (S₁S₂), 'Natsudaidai' (SfS₂), 'Tosa Buntan' (S₁S₃), clementine (S₃S₁1), 'Hirado Buntan' (S9S₁0), andso on. Frequency of S_n alleles, except for Sf allele, was 16.4% for S₁, 11.6% for S₂, 11.8% for S₃, 10.6% forS₄, 5.1% for S₅, 5.7% for S9, 2.9% for S₁0 and 13.7% for S₁1. Among Japanese cultivars and accessions withthe determined S alleles, those with S₄ allele were considered to originate from 'Kunenbo' tangor (CitruS_nobilis) or hybrids with 'Kunenbo' in their pedigrees. The Japanese c