Effects of shading and waterlogging following anthesis on starch synthesis and dry matter accumulation in wheat grain

Focusing on the reduced wheat yield caused by continuous rain following anthesis in the middle and lower reaches of the Yangtze River, a pot experiment was designed to investigate the effects of shading and waterlogging on starch synthesis and dry matter accumulation in wheat grains, to provide information regarding adverse resistance cultivation and stable yield of wheat in the area. Two wheat varieties - 'Yangmai 18' (waterlogging-insensitive type) and 'Wanmai 52' (waterlogging-sensitive type) - that are domain varieties in the Yangtze River Basin of China were selected to investigate the effects of 7-, 11-, and 15-day shading and waterlogging treatments following anthesis on starch synthesis and dry matter accumulation in wheat grains. The results indicated that there were no significant differences between the control and shading and waterlogging treatments in terms of the activities of adenosine diphosphate-glucose pyrophosphate (AGPase), soluble starch synthase (SSS), and bound starch synthase (GBSS) in wheat grains during the earlier grain-filling stage (10-15 days after anthesis). However, with the development of the grain-filling process, the difference between the control and shading and waterlogging treatments increased. In the mid-grain-filling stage (20 days after anthesis), when the activities of the three key enzymes were highest. The 11-and 15-day shading and waterlogging treatments decreased the activity of AGPase in wheat grain by 1% and 10% for 'Yangmai 18', and by 11% and 24% for 'Wanmai 52', respectively. Further, the activity of SSS was decreased by 5% and 11% for 'Yangmai 18', and 9%, 32% for 'Wanmai 52', respectively, compared with the control. In addition, the activities of SSS and GBSS under 11-and 15-day shading and waterlogging treatments were significantly lower than those in the control during the late grain-filling stage. Simulating the process of starch accumulation and grain filling with a Logistic equation showed that compared with the control, the shading and waterlogging treatments shortened the duration of the slow increasing stage and decreased the average grain-filling rate, average and peak starch accumulation rates, and cumulative wheat starch and dry matter amounts. Simultaneously, the shading and waterlogging treatments decreased the grain number and 1000-kernel weight of wheat, thereby lowering the yield. The extented shading and waterlogging treatments duration induced a decline in the activities of SSS and GBSS as well as the starch and dry matter accumulation amount in wheat grains and yield. The waterlogging-insensitive variety 'Yangmai 18' showed slight decreases compared with the waterlogging-sensitive variety 'Wanmai 52' in each index. Shading and waterlogging stresses following anthesis of wheat decreased the activities of AGPase, SSS, and GBSS and affected the starch and dry matter accumulation in wheat grains, thereby leading to yield loss.