Productive panicles per plant in hybrids are less than that in pure line cultivars is the main reason why competition heterosis of grain yield is not conspicuous in japonica rice (Oryza sativa L.). In order to improve the trait of hybrids, we detected static loci and dynamic loci affecting tiller numbers by using unconditional and conditional quantitative trait loci (QTL) mapping methods in this study. Tiller numbers were recorded every 14 days until maturity across two environments in 254 recombinant inbred lines (RILs) and parents. Genetic effects for tiller number at different measuring stages were estimated by the best linear unbiased prediction method. Thirteen unconditional additive QTLs were identified at nine stages. For the identical loci detected at various stages, positive alleles came from the identical parent. Seven of the 13 detected conditional additive QTLs were discovered from stage 1 to stage 4, when Xiushui 79 carried positive alleles of tiller number in qTN4 and qTN7.1, and C Bao carried positive alleles in qTN2.1, qTN5.1, qTN5.2, qTN9.1 and qTN10. The remaining six loci (qTN2.2,qTN3, qTN8.1, qTN8.2, qTN11.1 and qTN11.2) were detected between stage 5 and stage 9 when tiller number decreased. Except for qTN8.2, alleles decreasing tiller mortality came from Xiushui 79. For the 13 detected conditional QTLs, the numbers of elite alleles contained in a line had high significant positive correlation with its productive panicles per plant (r = 0.347**). These results indicated that tiller morphogenesis and mortality were controlled by different loci, and it is possible to enhance productive panicles per plant by pyramiding the elite alleles acting at different stages.
Key words: Rice (Oryza sativa L.), tiller, morphogenesis, mortality, quantitative trait loci (QTL) mapping.
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