Chlorophyll Content and Chlorophyll Fluorescence Kinetics Parameters of Flag Leaf and Their Gray Relational Grade with Yield in Wheat

Abstract

Drought stress impacts photosynthetic characteristics and results in a diminished output in wheat (Triticum aestivum L.). In the variety screening and breeding of wheat for high photosynthetic efficiency and drought resistance, indices for the assessment are of great importance. Although a few investigators have studied the physiological mechanism of photosynthesis on the basis of the chlorophyll fluorescence kinetics parameters with several wheat varieties, the relationships between these parameters and grain yield were not completely clear. The inheritance of chlorophyll related traits under different water conditions has not been reported, especially using genetic populations. To dissect the dynamics of photosynthetic characteristics and the heritabilities of chlorophyll content and chlorophyll fluorescence kinetics parameters in wheat, the authors have constructed a set of recombi-nant inbred lines (RILs) through crossing a highly drought-resistant variety, Hanxuan 10, and a high-yielding variety Lumai 14 grown in irrigated areas. In this study, 305 RILs of F8 generation were evaluated in well-watered and rainfed (drought stress) en-vironments, and traits of chlorophyll content and 7 chlorophyll fluorescence kinetics parameters in flag leaves were measured at flowering and filling stages. Most of the mean values of traits showed substantial transgressive segregation in the RILs, and the variation coefficients ranged from 1.12% to 67.05% under both water regimes. All traits measurements except for Fo and Fo/Fm in the RILs and their parents were lower under rainfed condition than under the well-watered condition. The chlorophyll content and the chlorophyll fluorescence kinetics parameters were more stable in Hanxuan 10 than in Lumai 14. Significantly positive correla-tions were observed in chlorophyll content between either water conditions or growth stages, and the correlation coefficients ranged from 0.499 (P 0.01) to 0.717 (P 0.01). However, correlations among the chlorophyll fluorescence kinetics parameters were complex, of which the largest correlation coefficients (more than 0.994) were observed between Fm and Fv and between Fo/Fm and Fv/Fm. Among all the traits tested, chlorophyll content had the highest heritability that was no less than 0.81 in both treatments. According to the primary estimates, most traits under rainfed condition were controlled by more genes than under well-watered condition. For instance, the maximum genes, totally 34, were detected for Fv/Fo at filling stage under rainfed condition; 33 genes were detected for Fv at filling stage under rainfed condition and for Fv/Fm and Fo/Fm at flowering stage under rainfed condition; 32 genes were found for Fm at filling stage under rainfed condition. The gray relational grade analysis indicated that Fv, Fm, and the area between curves of Fo and Fm at filling stage made important impacts on the grain yield. Therefore, they are considered as important indices in the selection of drought tolerance and high photosynthetic efficiency in wheat.