Segregation of Self-incompatible Hybrid Seedlings in Crosses with Grapefruit and possible RAPD Markers for the S Gene Alleles

To search for DNA markers linking with self-incompatibility gene (S) alleles of grapefruit, precociousflowering seedlings derived from 18 Citrus accessions crossed with grapefruit was examined for self-incompatibility. Self-incompatible and self-compatible seedlings segregated in 11 of the 18 crosses. Based on the result that the seven crosses did not segregate self-incompatible seedlings, it was suggested that self-incompatible 'Bansei Siam Buntan' and 'Hirado Buntan' pummelos share one of two their incompatibility S_" alleles with semi-self-compatible grapefruit, i.e., it was estimated that grapefruit has an S genotype of either S₁S₉ or S₁S₁₀. RAPD analysis was carried out with two progenies segregating seedlings with an expected ratio of 1:1 for self-incompatibility and self-compatibility. Forty-five DNA fragments amplified with 28 primers and 28 DNA fragments amplified with 13 primers differentially expressed in the self-incompatible and self-compatible seedlings derived from the crosses of 'Kawachi Bankan' x 'Foster Pink' grapefruit and 'Shishiyuzu' X 'Foster Pink', respectively. Further analyses of these possible DNA markers for self-incompatibility alleles of grapefruit may contribute to the development of seedless citrus breeding.