QTL analysis for flag leaf characteristics and their relationships with yield and yield traits in rice

Photosynthesis of carbohydrate is the primary source of grain yield in rice (Oryza sativa L.). It is important to genetically analyze the morphological and the physiological characteristics of functional leaves, especially flag leaf, in rice improvement. In this study, a recombinant inbred population derived from a cross between an indica (O. sativa L. ssp. indica) cultivar and a japonica (O. sativa L. ssp. japonica) cultivar was employed to map quantitative traits loci (QTLs) for the morphological (i.e., leaf length, width, and area) and physiological (i.e., leaf color rating and stay-green) characteristics of flag leaf and their relationships with yield and yield traits in 2003 and 2004. A total of 17 QTLs for morphological traits (flag leaf length, width, and area), 6 QTLs for degree of greenness and 14 QTLs for stay-green-related traits (retention-degrees of greenness, relative retention of greenness, and retention of the green area) were resolved, and 10 QTLs were commonly detected in both the years. Correlation analysis revealed that flag leaf area increased grain yield by increasing spikelet number per panicle. However, the physiological traits including degree of greenness and stay-green traits were not or negatively correlated to grain yield and yield traits, which may arise from the negative relation between degree of greenness and flag leaf size and the partial sterility occurred in a fraction of the lines in this population. The region RM255-RM349 on chromosome 4 controlled the three leaf morphological traits simultaneously and explained a large part of variation, which was very useful for genetic improvement of grain yield. The region RM422-RM565 on chromosome 3 was associated with the three stay-green traits simultaneously, and the use of this region in genetic improvement of grain yield needs to be assessed by constructing near-isogenic lines.