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Net photosynthesis rate and drought resistance in wheat need to be improved to enhance overall wheat productivity. Association mapping was used to explore the potential QTLs associated with net photosynthesis rate (Pn), thousand-kernel weight (TKW), biomass plant -1 (BMPP) and grain yield plant -1 (GYPP) under two water conditions and their drought indices, i.e. stress tolerance index (STI) and stress susceptibility index (SSI) in wheat using 269 whole-genome SSR markers in 59 winter wheat genotypes. Large numbers of marker-trait associations (MTAs) were detected for photosynthesis and yield related traits under both water conditions and related drought tolerance indices in both seasons. However, the number of significant associations reduced greatly when Bonferroni correction (FPDR) test was applied. Single marker, i.e. Xpsp3123-7D was associated with multiple traits across moisture conditions as well as growth seasons. Xgwm182-5D was stably associated with TKW under water-stressed conditions and with GYPP under well-watered conditions, respectively in both seasons. Xcfd33-6D was consistently linked with BMPP in both seasons under well-watered condition. A Total of 28 associations for the drought tolerance indices of those phenotypic traits qualified FPDR test. Of these, Xpsp3123-7D was consistently associated with the two drought indices of the traits in two seasons. The markers Xwmc707-4A and Xgwm182-5D were stably associated with stress susceptibility index (STI) of BMPP and stress tolerance index (STI) of TKW, respectively across two seasons. These putative QTLs, especially Xpsp312-7D can be the key targets to improve photosynthetic efficiency and yield potential of bread wheat in rainfed ecosystem.

Improvement in activation of Rubisco by Rubisco activase can potentially enhance CO2 assimilation and photosynthetic efficiency in plants. The three homoeologous copies of TaRca2-α were identified on chromosomes 4AL, 4BS and 4DS (TaRca2-α-4AL, TaRca2-α-4BS, and TaRca2-α-4DS) in bread wheat. Expression patterns of the three copies at heading (Z55), anthesis (Z67) and grain-filling (Z73) stages were investigated through qRT-PCR analyses in a panel of 59 bread wheat genotypes and their effects on net photosynthesis rate (Pn), biomass plant-1 (BMPP) and grain yield plant-1 (GYPP) were further explored. Different but similar expression patterns were observed for the three copies of TaRca2-α at the three growth stages with highest expression at grain-filling stage. TaRca2-α-4BS expressed higher at the three stages than TaRca2-α-4AL and TaRca2-α-4DS. The 59 genotypes could be clustered into three groups as high (7 genotypes), intermediate (41 genotypes) and low (11 genotypes) expression based on the expression of the three copies of TaRca2-α at three growth stages. Significant variations (P<0.01) were observed among the three groups of bread wheat genotypes for Pn, BMPP and GYPP. Generally, the genotypes with higher TaRca2-α expression also showed higher values for Pn, BMPP and GYPP. The expressions of the three copies of TaRca2-α at heading, anthesis and grain-filling stages were positively correlated with Pn, BMPP and GYPP (P<0.01) with stronger association for TaRca2-α-4BS at grain-filling stage. These results revealed that the expression of TaRca2-α contribute substantially to Pn, BMPP and GYPP, and suggested that manipulating TaRca-α expression may efficiently improve Pn, BMPP and GYPP in bread wheat and detecting TaRca-α expression levels with emphasis on TaRca2-α-4BS may be a positive strategy for selection in improving photosynthetic efficiency and grain yield of bread wheat.