Reexamination of Self-incompatibility Genotypes in the Japanese Pears : 'Choju', 'Kimizukawase', 'Meigetsu', and 'Ichiharawase'

Abstract

Self-incompatibility genotypes (S-genotype) were reexamined in the Japanese pear 'Choju', 'Kimizukawase', 'Meigetsu', and 'Ichiharawase'. The S-genotypes of the former 2 cultivars are designated as S₂S₅, whereas those of the latter 2 cultivars are S₁S₅. 'Choju' and 'Kimizukawase', which are cross-incompatible in both directions, possessed the S₁- and S₅-allele associated proteins (S-protein) in their styles. PCR (polymerase chain reaction) amplifications of self-incompatibility genes (S-gene) also revealed the presence of S₁- and S₅-gene fragments in both cultivars. Thus, the S-genotypes of 'Choju' and 'Kimizukawase' were confirmed to be S₁S₅, but not S₂S₅. 'Meigetsu' and 'Ichiharawase' were compatible with 'Choju' ; their styles contained the S₁-protein but not the S₅-protein. PCR amplification also suggested the absence of S₅-gene in both cultivars. These results together with those in the literature on the appearance of F₁ individuals with pollen cross-incompatibility with 'Meigetsu' indicate that the S-genotypes of 'Meigetsu' and 'Ichiharawase' are S₁S₇ or S₁S_x (S_x indicates an allele other than S₁ to S₇).