Identifying neutral allele Sb at pollen-sterility loci in cultivated rice with Oryza rufipogon origin

Pollen sterility is commonly found in the intra-specific hybrids of indica and japonica rice, which is one of the main constrains for the utilization of heterosis between indica and japonica. Six loci controlling the pollen sterility of F₁ between indica and japonica have been identified from previous studies. Neu-tral alleles at each locus are potential to overcome the F₁ pollen sterility associated with the locus. Therefore, exploitation and utilization of neutral alleles are of significant importance. The present re-search was based on fine mapping of the F₁ pollen-sterility gene Sb and the abundant genetic diversity of Oryza rufipogon Griff. indigenous to Gaozhou, Guangdong Province (referred to as Gaozhou wild rice). Crosses were made using Taichung65 (with the genotype of S_b^jS_b^j and referred to as E₁) and its near-isogenic line of F₁ pollen sterility gene Sb (with the genotype of S_bⁱS_bⁱ, E₂) as female parents, and 12 different accessions of Gaozhou wild rice as male parents. F₁ pollen fertility was examined to identify the materials having the neutral alleles at the F₁ pollen-sterility locus. Segregation of 4 molecular markers tightly linked with the Sb locus was analyzed in the F₂ populations derived from the F₁s car-rying the neutral gene. The pollen fertility related to the 3 genotypes of the molecular markers was also checked by statistical test to determine whether it was consistent with the hypothesis. The results showed that the pollen fertility of two F1s from one accession of Gaozhou wild rice (GZW099) with E₁ and E₂ was (89.22±1.07)% and (85.65±1.05)%, respectively. Both of them were fertile and showed no significant difference by t-test. Segregation of the 3 genotypes of the 4 molecular markers followed the expected Mendelian ratio (1:2:1) in the F2 populations. There was no significant difference for the av-eraged pollen fertility of the plants related to the 3 genotypes, suggesting that no interaction exists between the alleles at the Sb locus in GZW099 and Taichung65 or E₂. Evidentially, GZW099 carried the neutral gene (named S_bⁿS_bⁿ) at the Sb locus, which provides valuable theoretical basis and resources for further studying and overcoming the sterility of indica-japonica hybrids.