Effects of shading stress applied at the early reproductive growth stage on the photosynthetic characteristics, morphological traits, and yield components of wheat

Background/Question/Methods Light intensity is an important factor that affects crop growth and yield. Unfortunately, In North China Plain, with the development of industry, air pollution (haze) or cloudy is getting more and more serious. PM2.5 frequently exceeds the Chinese Grade II standard (75 µg/ml). The decrease of light intensity, which was caused by haze, has an adverse effect on the formation of wheat yield during season of wheat growth. Cloudy/rainy weather and fog-haze events often appears during the early reproductive growth stage of winter wheat, Understanding the effects of shading stress during microspore development stage on grain number and morphological characteristic of winter wheat could improve grain yield. This paper conducted field and pot experiments (2015-2016) on the responses of 14 winter wheat to different levels of shade tolerance under blocking 98% of natural light. Among them, six winter wheat cultivars were subjected to shading stress (blocking 98% of natural light, six shading duration treatments from 1 to six days) during microspore development stage. Full natural light was as a control.

Results/Conclusions The results showed that grain number of main stem was decreased under shading stress during microspore development stage for all the cultivars. Grain yield, plant height, biomass, net photosynthesis, main-stem chlorophyll content were significantly decreased with the increase of shading stress time. However, the total tiller numbers were increased. There were significant differences in grain yield among six winter wheat cultivars after six days shading stress. The grain yield of Jimai32 and Henong825, shade-tolerant cultivars, was decreased by only 17.3% and 14.2%, respectively, whereas that of Kenong9204 and Liangxing99, shade-sensitive cultivars, was decreased by 74.9% and 91.4%, respectively. The results indicated that the microspore development stage were the developmental stage that were the most sensitive to shading stress. Reduction in grain number was the main factor for grain yield loss under shading stress. Shade-tolerant cultivars have a more effective shading defense and compensation mechanisms including tiller rapid development and rapid photosynthesis recovery. It will provide important information for breeding wheat with response strategies under haze.