Breeding for elevated carbon dioxide responsive cultivars and identification of associated QTLs in rice

Carbon dioxide is one of the most important factors in plant growth and development. With the increasing CO2 levels in the atmosphere, this study aims to develop a suitable screening protocol in selecting genotypes with responsive trait and to identify the quantitative trait loci governing e CO2 tolerance rice. An initial of 2700 DQP 43 RILs were screened for two seasons under elevated CO2 using a modified chamber with Day/Night CO2 Monitor and Controller and walk-in plant growth chamber (Conviron, USA) supplied with CO2 at an average of 800 ppm. Twenty-one and 50 genotypes were selected during the first and second rounds of screening, respectively. A field st up with the 50 DQ43 lines were grown under normal (aCO2) irrigated condition. Exposure to elevated CO2 showed significant effect on both vegetative and reproductive stages of growth among the selected genotypes. Plant height, length of flag leaf, and culm diameter have positive effect with elevated CO2. During the productive stage, exposure to elevated CO2 have positive effect with elevated CO2. During the reproductive stage, exposure to elevated CO2 resulted to delay in flowering with increased unfilled grains and discolored spikelets. Panicle count and length, grain per panicle, and grain weight per plant however were positively affected by eCO2. Considering both vegetative and reproductive traits, five promising lines under eCO2 were selected, namely GSR-IR2-DQ43-EC10-EC3, GSR-IR2-DQ43-EC15-EC1, GSR-IR2-DQ43-EC4-EC1, GSR-IR2-DQ43-EC10-EC2 and GSR-IR2-DQ43-EC11-EC2. Four QTLs were identified in response to eCO2 namely qRPL2 and qRPL2.1 found to be associated with panicle trait while qR100F1w1 and qRGWtP1 were associated with days to 100 present flowering grain weight per plant, respectively. Seventy-eight candidates genes were identified from the four QTLs. Nine are considered as the putative genes related to eCO2.