Twenty-four alleles at twelve quantitative trait loci act additively to control tiller angle in cultivated rice

Tiller angle, controlled by quantitative trait loci (QTL), is crucial for achieving ideal plant architecture in rice, which affects its final yield values. It is important to understand the genetic mechanisms underlying tiller angle when breeding new plant-type varieties. To uncover the genetic regulation mechanisms in cultivated rice, we performed QTL analysis using a recombinant inbred line (RIL) mapping population consisting of 219 lines developed by crossing two rice cultivars, Lemont and Yangdao4. The angle between the side tiller (ST) and the horizontal ground was measured as a tiller angle-related trait in QTL analysis. Twenty-three QTLs responsible for ST-ground angle were detected using multiple interval mapping in four mapping environments. A major QTL, qTA9 , was detected on chromosome 9, which explained 12.9, 39.8, 37.9, and 28.3% of the phenotypic variation in the four mapping environments, respectively. Another QTL, qTA8 , with a relatively large effect, was detected on chromosome 8. The other 21 QTLs explained < 10% of the phenotypic variation individually. These 23 detected QTLs were localized in 12 loci that act additively to influence tiller angle as demonstrated by regression analysis: plants carrying more ST-ground angle-increasing alleles at the 12 loci had larger ST-ground angles than those carrying more angle-decreasing alleles. Multiple comparison tests indicated that if marker-assisted selection was used in breeding, selecting five loci randomly from the 12 loci was enough to guarantee a phenotype with a ST-ground angle of over 78°. These results reveal the sophisticated genetic mechanisms controlling tiller angle in cultivated rice.