Improving bridge effect to overcome interspecific hybrid sterility by pyramiding hybrid sterile loci from Oryza glaberrima

Abstract

In order to evaluate the genetic effect caused by hybrid sterile loci, NILs with O. glaberrima fragment at six hybrid sterile loci under O. sativa genetic background (single-locus-NILs) were developed; two lines harboring two hybrid sterile loci, one line harboring three hybrid sterile loci were further developed. A total of nine NILs were used to test cross with O. sativa recurrent parent, and O. glaberrima accessions respectively. The results showed that the sterility of pollen grains in F₁ hybrids deepened with the increase of the number of hybrid sterile loci, when the nine lines test crossed with O. sativa recurrent parent. The F₁ hybrids were almost completely sterile when three hybrid sterile loci were heterozygeous. On the other hand, the single-locus-NILs had limited bridge effect on improving pollen grain fertility of interspecific hybrids. Compared single-locus-NILs, the multiple-loci-NILs showed increasing effect on pollen fertility when test crossing with O. glaberrima accessions. Further backcrossing can improve the fertility of pollen grain and spikelet of interspecific hybrids. The optimal solution to improve the fertility of interspecific hybrid can be utilization of pyramiding bridge parent plus backcrossing. This report has potential for understanding the nature of interspecific hybrid sterility, and overcoming the interspecific hybrid F₁ pollen grain sterility between O. sativa and O. glaberrima.

Figure 1

Genetic background screen of six NILs with single hybrid sterile allele from O. glaberrima using C6AIR. Twelve chromosomes of rice are labelled from 1 to 12 and the triangles indicated the positions of the centromere. The reference genome is O. sativa DJY1. The circle indicate the positions of the target locus. The black lines indicated the positions of the SNP with homozygous genotypes where genomic fragments of the donor parent were introgressed, red lines indicated the positions of the SNP with heterozygous genotypes, and the genotypes of the rest genomic regions were the same as the recurrent parent DJY1.