Linkage Analysis of SPR3 Locus and Pi45(t), and Evaluation of Yield-Related Traits Using Near Isogenic Lines From a Cross Between Japonica Rice

Although traditional rice varieties and wild rice species exhibit vast genetic diversity, the transfer of useful genes to modern varieties is often hampered by linkage drag. In this study, the previously identified blast resistance locus Pi45(t) from a cross between ‘Ilpumbyeo’ and ‘Moroberekan’ was linked to the spreading-type panicle caused by the SPR3 locus. Using InDel4 and RM17579 linked to the Pi45(t) and the SPR3, respectively, the distance between the two loci was estimated to be 6.9cM. This suggests a tight, yet incomplete linkage and provides the opportunity to utilize Pi45(t) in breeding programs without including SPR3. Two groups based on the genotype at the SPR3 locus were assembled; the CLosed Panicle (CLP) and SPReading panicle (SPR) groups, with lines which were homozygous for the Ilpumbyeo and Moroberekan alleles, respectively. A comparison between the traits of CLP and SPR groups revealed a decrease in 1000-grain weight and length and an increase in spikelets per panicle and secondary branches in the SPR group. This complicates selection against SPR3 as it is not clear whether these quantitative trait loci are linked to either SPR3 or Pi45(t). Re-evaluation of these traits using lines recombinant at the two loci would be necessary to clarify this issue.