Effect of low temperature stress on physiological characteristics of flag leaf and its relationship with grain yield during panicle primordium differentiation stage of early rice

The effects of low temperature stress on physiology and yield characteristics of early rice in Jiangxi Province as driven by artificial environmental controls were studied in this paper. The paper also analyzed the relationship of physiological characteristics and yield components with yield of early rice under low temperature (22 ℃/17 ℃) in the study area with gray correlation analysis. The normal daytime temperature in the region was 30 ℃ and that of night time was 25 ℃. With prolonged low temperature treatment, chlorophyll a, chlorophyll b and carotenoids contents of early rice leaves rose initially and dropped later. Maximum photosynthetic rate, light saturation point and initial light use efficiency tracked a downward trend according to photosynthetic light response curves. Light compensation point was apparently on the rise. Fluorescence parameters of qP, ETR, F_v/F_m had an early-increasing/later-decreasing tendency. Conversely, qN reached its maximum value after low temperature stress for 6 d. While activities of SOD, POD and contents of MDA and soluble protein had an early rise and later drop, CAT activity followed a declining trend. Yield, spike length, seed setting rate, spike rate, grain weight and other yield traits followed a decreasing tendency. Based on gray correlation analysis, in relation to yield, the rank of correlation degree was as follows: grains per panicle > spike length > secondary branch number > primary branch number > 1000-kernel weight > CAT, and the correlation degrees of these traits were all greater than 1. The physiological traits, such as initial light use efficiency, light saturation point, ETR, F_v/F_m, chlorophyll a/chlorophyll b also had greater correlation with early rice under low temperature. These physiological traits could be used as indicators to evaluate early rice yield under low temperature stress.