Characterization Of Three Neutral Alleles (f5, F6 From Dular, S5 From 02428) Conferring Wide-compatibility And Fine-mapping Of F5-Du

Wide-compatibility varieties (WCVs) are a special class of rice germplasm that is able to produce fertile hybrids when crossed to both indica and japonica subspecies. Previous studies determined Dular and 02428 as two WCVs, and identified a number of QTLs as having large effects on fertility of inter-subspecific hybrids. In this study, we developed five near isogenic lines (NILs) for three of the QTLs, f5, f6, and S5, by backcrossing and marker-assisted selection, using Dular and 02428 as the donors and Zhenshan 97 as the recipient. Three of the NILs each carried one introgressed allele, and 2 NILs each carried two introgressed alleles in combinations. The NILs were test-crossed to an indica tester Nanjing 11 and a japonica tester Balilla. The main results are as follows:1. The selected NILs, designated ZS(f5-Du/f5-ZS), ZS(f6-Du/f6-ZS), ZS(S5-08/S5-ZS), ZS(f5-Du/f5-ZS, f6-Du/f6-ZS) and ZS(f5-Du/f5-ZS, 55-08/S5-ZS), were respectively with 98.75%, 98.75%, 97.92%, 96.67%, and 96.67% recovery of the recurrent parent genome. In particular, these NILs were homozygous for the Zhenshan 97 alleles for markers representing all the regions known to harbor loci (or QTLs) for indica/japonica hybrid sterility, as reported in previous studies.2. When the NILs were test-crossed to indica tester Nanjing 11, all the crosses produced normal fertile hybrids as the control cross, Zhenshan 97×Nanjing 11. And all the three genotypes of the self-pollinated progenies from each of the NILs also showed normal fertility. In addition, no distorted segregations of the three genotypes were observed. Thus, all three alleles that were transferred to Zhenshan 97 from the WCVs had complete compatibility with the indica alleles.3. In the compatibility tests to japonica variety, comparison between the two genotypes for each of the three loci showed that the two genotypes at the f5 locus had the largest differences in both pollen and spikelet fertility; the f5-Du allele could increase the pollen fertility (I₂-KI stainability) by more than 50% and the spikelet fertility by over 20%. While differences between the two genotypes at the other two loci (f6 and S5) were not significant.4. Test-crosses of two-locus genotypes also showed that f5 was the only locus causing statistically significant difference in pollen fertility. All the two-locus genotypes involving the f5-Du allele had much higher pollen fertility than ones having the f5-ZS allele. In addition, test-crosses of the two-locus genotypes also detected the effects of the other two...