Production of Homozygous S1 Seedlings for S Gene in 'Hirado Buntan' Pummelo (Citrus grandis Osbeck) and Determination of the S Alleles (S_9 and S_10) by Pollination with the S_1 Seedlings to Citrus Cultivars

Abstract

Gametophytic self-incompatibility (SI) in Citrus is known in pummelo, mandarin and many hybrid cultivars with pummelo in their pedigrees. What seems to be lacking, however, is determination of allelic vari- ation in SI gene (S) and the genotypes of self-incompatible and semi self-incompatible cultivars. In previ- ous studies, S genotypes of several Citrus cultivars were estimated on the basis of segregation distortion for Got-3 gene in F1 progenies between these cultivars. In this study, S1 seedlings were produced from self- pollinated 'Hirado Buntan' pummelo, and homozygous S1 seedlings for the S gene were determined by the pollination with 'Hirado Buntan'. Then, the homozygous S1 seedlings were pollinated with the homozygous S1 seedling (SaSa) each other and classified them into two genotype groups of SaSa and SbSb. The ten culti- vars, whose S genotypes were predicted on the basis of joint segregation analysis with Got-3 gene in their progenies, were pollinated with the homozygous S1 seedlings (SaSa or SbSb). Pollen tube behavior in the style of the ten Citrus cultivars after pollination with the Sa or Sb pollen led to the conclusion that 'Hirado Buntan' has S9 and S10 alleles. Furthermore, pollen tube arrest in the style of self-compatible 'Kabusu' sour orange pollinated with S9 pollen suggested that the genotype of 'Kabusu' is SfS9. Inscrutably, neither S9 nor S10 alle- les were found in a group belonging to the Hirado pummelo line, which started from seeds sown by the 11th feudal load Terasu Matsura of the domain of Hirado. This fact supported the two origins of Hirado pummelo plants described in the literature, and indicated the association of multiple seed and/or pollen parents with different S alleles to the original seed production.