Identification of quantitative trait loci for δ13C and productivity in irrigated lowland rice

Stable carbon isotope ratio (delta C-13) in plants has been suggested as a useful indicator for cumulative Ci/Ca signature in a leaf, water use efficiency, and crop productivity, and is known to have genotypic variation in rice (Oryza sativa L.). We conducted a field study to identify quantitative trait loci (QTLs) for delta C-13 and other related leaf traits, such as leaf N, specific leaf area, and SPAD value, using recombinant inbred lines derived from an indica X japonica cross grown under flooded conditions. We also examined the genetic associations of delta C-13 with yield, yield components, and biomass productivity. Putative QTLs for delta C-13 were identified on chromosomes 2, 4, 8, 9, 11, and 12 across plant parts, stages, and years. Differential expression of QTL for delta C-13 among stages suggests that each QTL had different functions by stages. The QTLs for delta C-13 were associated with a few colocated QTLs for leaf traits indicating that their physiological and genetic associations with leaf traits may be complex. Values of delta C-13 at maturity were negatively correlated with harvest index and grain yield. However, genetic association of these traits could not be clarified due to the absence of co-located QTLs. Further examination would be useful to elucidate the physiological and morphological functions of QTLs for delta C-13 found in this study.