Seedlings obtained from crosses with Citrus species and cultivars showed precocious flowering in spring after seed germination in autumn. Male-sterile anthers were observed in the flowers of seedlings from seven crosses. On the basis of segregation analysis for male sterility in these progenies, male-sterile genotype was estimated to be (S)r1r1R2r2r3r3 for male sterile 'HY16', (S)r1r1r2r2R3r3 for male sterile 'Kiyomi' and (F)r1r1R2R2R3r3 or (F)R1r1R2R2r3r3 for male fertile 'Foster Pink' grapefruit. Here, male sterility is a recessive character; r2 and r3 are complementary genes with upper stream expression of r1, and r1 is an epistatic gene to r2 and r3 genes. Male sterile seedlings appear when r1 is recessive homozygous (r1r1) and either r2 or r3 is recessive homozygous (r2r2 or r3r3). A population of 101 individuals from the cross of 'HY16' × 'Foster Pink', in which male sterile and male fertile seedlings segregated in a 1:1 ratio, was chosen for mapping the R gene with RAPD markers. Reproducible polymorphisms of amplified DNA fragments were obtained; 260 RAPD primers were tested by means of bulked segregant analysis. Five RAPD markers amplified in most of male-fertile individuals and 'Foster Pink'. On the other hand, two RAPD markers were found in most of male-sterile individuals and 'Foster Pink'. The linkage analysis showed that the five markers flanked with R1 or R3 gene with the closest distance of 8.4 cM in grapefruit and the two markers flanked with r1 or r3 gene with the closest distance of 15.5 cM in grapefruit.
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