THE HIGH-LEVEL OF WIDE COMPATIBILITY OF VARIETY DULAR HAS A COMPLEX GENETIC-BASIS

Wide-compatibility varieties (WCVs) are a special class of rice germpl asm that is able to produce fertile hybrids when crossed to both indic a and japonica rice varieties. WCVs may differ greatly in their spectr um and level of compatibility. The objective of this study was to dete rmine the genetic basis of wide-compatibility conferred by 'Dular', a landrace variety from India that has demonstrated a high level of wide -compatibility in previous studies with a broad range of indica and ja ponica varieties. A three-way cross ('Balilla/Dular//Nanjing 11') was made and the resulting FI population evaluated in the field for spikel et fertility. A total of 235 plants from this population was assayed i ndividually for restriction fragment length polymorphisms (RFLPs) at 1 59 marker loci covering the entire rice genome at regular intervals. Q uantitative trait locus (QTL) analysis identified 5 loci, located on c hromosomes 1, 3, 5, 6 and 8, as having significant effects on hybrid f ertility, which jointly explained 55.5% of the fertility Variation in this population. The QTL on chromosome 5 (f5) showed the largest effec t on hybrid fertility, followed by those on chromosomes 6 (f6), 3 (f3) and 1 (fl), with the one on chromosome 8 (fg) having the smallest eff ect. Genotypes each composed of an allele from 'Dular' and an allele f rom 'Nanjing 11' at four (f3,f5,f6 and f8) of the five QTLs contribute d to the increase of fertility in the population. In contrast, the gen otype composed of alleles from 'Balilla' and 'Nanjing 11' at the fifth locus (fl) was in the direction of increasing fertility. Analysis of variance using marker genotypes at the five QTLs as the groups detecte d two interactions involving four of the five loci, a 2-locus interact ion between f5 and f8 and a 3-locus interaction among f3, f5 and fd. T he level of hybrid fertility is the result of complex interactions amo ng these loci. The implication of the present findings in the utilizat ion of the wide-compatibility of 'Dular' in rice breeding programs is also discussed.