Shading under drought stress during grain filling attenuates photosynthesis, grain yield and quality of winter wheat in the Loess Plateau of China

In the Loess Plateau region of China, winter wheat often undergoes prolonged cloudy days without rain which may affect the grain yield and quality. This study examined the impacts of shading and drought conditions during the grain-filling period of winter wheat (Triticum aestivum L.) on photosynthesis, grain yield and quality traits in a greenhouse experiment. The imposed shading and irrigation-deficit treatments were corresponded with naturally cloudy weather in the rainfed area. Five shading treatments, 15 days shading (SD15); 12 days shading (SD12); 9 days shading (SD9); 6 days shading (SD6); and 3 days shading (SD3), and four irrigation treatments: full irrigation (I100); 75% of full irrigation (I75); 50% of full irrigation (I50); and 25% of full irrigation (I25), were applied after completion of flowering. The results showed that shading during grain filling decreased the grain yield and individual grain weight irrespective of the dry or wet conditions of the soil. Plant height increased with a decrease in shading duration to favour the efficient capturing of light. The reduction in the rate of photosynthesis was noted with an increase in the drought intensity. Shading significantly reduced the grain protein contents and increased the grain starch contents. In conclusion, shading for a long duration (SD15, SD12 and SD9) and drought stress (I25) during the grain-filling stage significantly decreased the yield and grain quality of winter wheat. The shading of few days without drought (I100: SD3, SD6 and SD9) improved the plant height, photosynthetic activity and increased the distribution of dry matter from vegetative organs to grains.