Quantitative trait loci for the number of grains per panicle dependent on or independent of heading date in rice (Oryza sativa L.)

Abstract

Both the heading date (HD) and the number of grains per panicle (GPP), which frequently correlate with each other, are important agronomic traits for rice. In this study, two sets of recombinant inbred lines (RILs) derived from crosses between Minghui 63 and Teqing (PMT) and Zhenshan 97 and Teqing (PZT), respectively, were used to dissect the genetic bases of the correlation between HD and GPP. GPP quantitative trait loci (QTLs) identified by conventional QTL analysis could be classified into two types, either dependent on or independent of HD regardless of the effect caused by flowering time. Conditional analysis detected only GPP QTLs independent of HD when the HD effect on GPP was eliminated. With conventional QTL analysis, eight and five GPP QTLs were detected in PZT and PMT, respectively. However, three and five QTLs were detected by conditional analysis. Five of eight were dependent on HD (type I QTLs) in PZT, and all QTLs identified in PMT were independent of HD (type II QTLs). Photoperiod response of qGPP7b near-isogenic lines confirmed that qGPP7b effects on GPP were caused by HD. The characteristics of type I and II QTLs related to their application in rice breeding are discussed.