Genotyping of Citrus Accessions with S9 and/or S10 Alleles for Self-incompatibility and Their Allelic Distribution

Jung Hee Kim, Mayumi Sato, Akira Wakana, Fuka Takamatsu, Kaori Sakai, Masayoshi Shigyo, Jun Ichiro Masuda

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Gametophytic self-incompatibility, one of the key characteristics for breeding seedless Citrus cultivars, occurs in pummelo (Citrus maxima), mandarin (Citrus reticulata), and their hybrid cultivars. Allelic variation in Citrus was reported for the self-incompatibility gene (S); however, S allele frequencies and S genotypes of full-and semi-self-incompatible cultivars have been reported for a small number of alleles. To extend our knowledge of S alleles, we tested 146 Citrus accessions, including 82 pummelo accessions, for S9 and S10 alleles. Each accession was pollinated with homozygous S1 seedlings of ‘Hirado Buntan’ pummelo (S9S9 and S10S10). The pollen tube growth arrest in the lower styles of their pollinated pistils indicated that four accessions, including ‘Hirado Buntan [Citrus maxima (Burm.) Merr.]’, have the S9 allele and five accessions, including ‘Hirado Buntan’, have the S10 allele. The percentage of accessions with the S9 allele was 3.2% (4 of 126 accessions examined), and the S9 allele frequency was 1.8% (4 of 217 alleles, excluding the Sf allele). The percentage of accessions with the S10 allele was 3.9% (5 of 127 accessions examined), and the S10 allele frequency was 2.3% (5 of 217 alleles, excluding the Sf allele). Japanese mandarin (another sources of S alleles) and its relatives had neither the S9 nor the S10 allele. Pummelo accessions had S9 and S10 alleles at higher rates of 2.9% (2 of 70 accessions examined) and 7.0% (5 of 71 accessions examined), respectively. ‘Kabusu’ sour orange (a pummelo-mandarin hybrid; Citrus aurantium) and ‘Kikudaidai’ (a sour orange relative; Citrus canaliculata) had S9 alleles. These results suggested that the two alleles originated from pummelo (the main sources of S alleles). The S genotypes with S9 and/or S10 alleles were fully determined in ‘Hirado Buntan’ (S9S10), ‘Kabusu’ sour orange (SfS9), the ‘Kikudaidai’ (S9S11) sour orange hybrid, and two local pummelo plants. The results of our study suggest that in comparison with the other S alleles reported, the pummelo plants with low frequencies of S9 and/or S10 alleles contributed to very low rates of evolution and development of Citrus species and cultivars during the long history of citrus cultivation, except for those generating sour oranges (Citrus auratinum), which are used as root stocks, and for flesh and rind processing and ornamental plants. Finally, we examined the degree of self-incompatibility between S9 and S10 alleles in the lower part of styles of S1 seedlings of ‘Hirado Buntan’ and Citrus accessions with S9 and/or S10 alleles. The result indicated no difference in the self-incompatibility reaction between the two alleles.

Original languageEnglish
Pages (from-to)807-822
Number of pages16
JournalHorticultural Science and Technology
Issue number6
Publication statusPublished - 2021

All Science Journal Classification (ASJC) codes

  • Horticulture


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