Effects Of Water Stress At Elongation And Heading Stages On Physiological Characteristics, Grain Yield And Quality Of Yangmai 20

Drought, waterlogging, alternate drought and waterlogging occur frequently in the middle and lower reaches of the Yangtze River Region from March to April. This is the period when the elongation and flowering of wheat plants take place and wheat plants are sensitive to moisture. Too low or high soil moisture levels may affect wheat growth and yield formation. In this study, a pot experiment, with Yangmai 20 as the variety, to investigate the effects of drought and waterlogging at elongation and heading stages on grain yield and yield components, grain quality, plant traits and physiological parameters. The experiment was done from 2013 to 2015 on the Experimental Farm of Jiangsu Provincial Key Laboratory of Crop Genetics and Physiology of Yangzhou University. The objective of this study was to develop the approaches of irrigation and drainage regulation and stress-relief for wheat plants at different growth stages. This study is of critical importance for providing theoretical support and practical guidance for anti-stress and high and stable production of wheat following rice. The main results were as follows:1. Moderate drought (soil moisture content less than 50% field capacity lasting 12 d) at elongation stage reduced the number of spike per plant by 45.32% and the number of grain per spike by 49.22%, increased the 1000-grain-weight by 17.97%. But the increase in grain weight was not able to make up for the reduction in the number of spike per plant and the number of grain per spike, leading to a significant decrease in grain yield by 55.34%. Mild drought and wet injury at elongation stage didn’t had significant effects on grain yield and its components. Waterlogging lasting 12 days at elongation stage reduced the number of spike per plant and 1000-grain-weight, and therefore the yield was reduced by 19.76%. Moderate drought at heading stage reduced the number of grain per spike and 1000-grain-weight, leading to a reduction of 40.56% in grain yield. The grain yield was reduced by 21.57% under mild drought at heading stage. The decrease in both the number of grain per spike and 1000-grain-weight could be the factors reducing grain yield. Wet injury and waterlogging at heading stage reduced grain yield by 9.71% and 10.24%, respectively. In order to prevent a substantial reduction in grain yield, moderate drought and waterlogging should be avoided at elongation stage, while any water stress must be avoided after heading.2. After the treatment of moderate drought at elongation stage, moderate drought and mild drought at heading stage reduced grain yield by 67.75% and 54.15%, respectively. After the treatment of mild drought at elongation stage, the mild drought and wet injury at heading stage reduced grain yield by only 11%. After the treatment of wet injury at elongation stage, mild drought at heading stage significantly reduced grain yield by 34.85%. In addition, grain yield was reduced by nearly 90% when waterlogging occurred at both elongation and heading stage. If moderate drought occurs at elongation stage, any water deficit must be avoided after heading. Besides, while waterlogging occurs at elongation stage, drought and longtime waterlogging at heading and anthesis stage must be avoided to prevent a substantial reduction in grain yield. The mild drought or wet injury at the elongation stage can significantly improve the drought tolerance and waterlogging tolerance, which could be used as a feasible way to reduce the water stress damage after anthesis.3. Moderate drought and waterlogging at elongation stage as well as waterlogging at heading stage decreased plant height by up to 20%. Wet injury at elongation stage and mild drought at heading stage had no significant effects on plant height.4. Moderate drought at elongation stage inhibited dry matter accumulation and yield formation of wheat significantly. The effects of wet injury at elongation and heading stage on grain weight were not significant, while waterlogging at elongation and heading stage significantly decreased grain weight and its proportion to total weight. The appropriate mild water stress at elongation stage didn’t have significant effects on dry matter accumulation and grain yield, which optimized the distribution of dry matter. But long-term waterlogging must be avoided after elongation stage.5. Under water stress conditions, stressful were engendered effects with increased senescence rate and protective enzyme activity of flag leaf within a short period of time. But the enzyme activity began to decline along with the stress time prolonged. The more serious the stress was, the faster enzyme activity decreased. The change of flag leaf MDA content lagged behind the SOD activity. It showed that plant removed free radicals and reduced MDA content by increasing senescence and protective enzyme activity, which played an important role in improving drought or waterlogging tolerance in wheat.6. Moderate drought at elongation stage increased grain protein content by 45.54% and the grain amylose to amylopectin ratio increased significantly, while amylopectin content decreased. Grain glutenin content and amylopectin content decreased significantly under wet injury at elongation stage. Waterlogging at elongation stage decreased grain protein and its components content and amylopectin content. Soil drought at heading stage increased grain protein content. Wet injury at heading stage reduced albumin, alcohol soluble protein content and amylopectin content significantly. Inordinate low or high soil moisture was not conducive to the improvement of grain quality. Maintaining the appropriate soil moisture content can improve the processing quality of wheat grain.7. When moderate drought occurs at elongation stage, irrigation should be done. Heading stage is the critical period of water requirement in wheat. When soil moisture content is lower than 60% field capacity, irrigation should be done to ensure flowering and grain filling. Soil moisture content should be controlled between 70% and 75% field capacity from elongation to heading stage. Drainage in time after rain and drop moisture anti waterlogging.