Gametophytic self-incompatibility, one of the key characters for seedless citrus production, is controlled by single codominant gene S known in pummelo, mandarin and their hybrid cultivars. However, little is known about S genotypes and S allele frequencies in Citrus cultivars. First, S genotypes and S allele frequencies of Citrus accessions were studied with S4 and S5 gene alleles of ‘Hassaku’ (C. hassaku hort. ex Tanaka) a putative hybrid between self-incompatible pummelo [C. maxima (Burm.) Merrill; syn. C. grandis Osbeck] and ‘Kunenbo’ (C. nobilis Lour. var. kunep Tanaka). About 200 Citrus accessions were pollinated with each of the homozygous S1 seedlings (S4S4 and S5S5) of ‘Hassaku’. Pollen tube arrest in the styles indicated that 19 of 202 (9.4%) accessions have an S4 allele and 12 of 191 (6.3%) accessions have an S5 allele. In pummelo, the rate of accessions with S4 allele was 1.4% (1/72), while that with S5 allele was 5.9% (9/76). This suggests that the two alleles are originated from pummelo and the allele frequency is 0.7% (1/144) for S4 and 5.9% (9/152) for S5. Except ‘Kunenbo’, all accessions with S4 alleles have their origin in Japan. These results suggest that self-incompatible ‘Kunenbo’ (S4S?) introduced from Southeast Asia to Japan about 600 years ago firstly generated satsuma mandarin (SfS4) and ‘Kabuchii’ (S4S?) about 400–500 years ago, followed by 16 S4-carrying cultivars including ‘Hassaku’ (S4S5) appearing as a chance seedling in Hiroshima in the nineteenth century.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Agronomy and Crop Science
- Plant Science