Mapping of QTLs for source and sink associated traits under elevated CO2 in rice (Oryza sativa L.)

Rice source- and sink-associated traits are important for grain yield and are sensitive to environmental conditions. The continuing increase of CO2 concentrations in the atmosphere will become a major challenge for rice growth and development in the future due to changes in our climate such as extremes in temperature. To guarantee food safety, novel genetic loci need to be identified for source- and sink-associated traits that are specifically expressed under elevated CO2 conditions. Eighty chromosome segment substitution lines carrying japonica (Nipponbare) chromosome segments in the indica (9311) background were used in this study. QTL analysis was conducted for source- and sink-related traits, including flag leaf length, flag leaf width, flag leaf fresh weight, flag leaf dry weight, primary branch number, secondary branch number, grain number per panicle, panicle weight per plant, chlorophyll a, chlorophyll b, and carotenoid contents, under ambient CO2 concentrations and free-air CO2 enrichment. A total of 49 QTLs for these traits were detected on chromosomes 1, 3, 5, 6, 7, 9, and 12 under the two conditions; the variance explained by these QTLs varied from 6.22 to 38.15%. Among these QTLs, 19 of them were detected under the natural field conditions and 30 were detected in the elevated CO2 conditions. In addition, 2 and 13 QTLs were specifically expressed in the natural and CO2-enriched conditions, respectively. Our findings have important implications on the utilization of germplasm resources for ensuring food security under elevated CO2 levels, especially for QTLs that were specifically detected under the elevated CO2 condition.