Estimation of self-incompatibility genotypes of Citrus cultivars with Got-3 allozyme markers

Self-incompatibility (SI) in Citrus is known in cultivars and plants of pummelo, pummelo relative, and mandarin; however, the detailed mechanism of self-incompatibility and the allelic diversity of the SI gene (S) are not known because of the presence of barriers such as nucellar embryony, male sterility, and a long juvenile phase. Thus, there is little information on S genotypes of Citrus cultivars at present. In this study, the S genotypes of Citrus cultivars were estimated with the aid of allozymes produced by a glutamate oxaloacetate transaminase isozyme gene (Got-3), which appeared to link to the S gene. Of twenty-two F ₁ progenies from eleven crosses and their reciprocal crosses with eight monoembryonic SI cultivars, including 'Banpeiyu' pummelo, three F ₁ progenies from three crosses and three from reciprocal crosses showed segregation distortion for the Got-3 gene, suggesting the presence of the same S alleles in the cultivars used for the reciprocal crosses. Defining the 'Banpeiyu' genotype as S ₁S ₂, the genotype was estimated as S ₁S ₃ for 'Tosa Buntan', S ₄S ₅ for 'Hassaku', S ₆S ₇ for 'Yuge-hyokan', and S ₁S ₆ for 'Shishiyuzu'. Further allozyme analyses for segregation distortion in progenies from eight crosses with eight monoembryonic SI cultivars suggested the possibility that 'Hyuganatsu' has S ₁ allele, while those from 15 crosses between the eight monoembryonic SI cultivars and five polyembryonic self-compatible cultivars suggested the possibility that 'Rough lemon' has S ₁ allele. The estimated genotypes, consisting of two of the nine alleles (S ₁ to S ₈ and S _f) in these Citrus cultivars, may be useful for further estimation and determination of S genotypes in Citrus cultivars and plants. JSHS