Effect Of Alternate Wetting And Drying Irrigation During Grain Filling On Rice Yield And Quality And Its Physiological Mechanism

Water shortage is a serious problem in China. Rice (Oryza sativa L.) is one of the most important food crops in this country and is also the largest water consumer in agriculture. The grain filling stage is the most important stage in which grain weight and quality are formed. Therefore, it would have great significance to develop water-saving agriculture and achieve high grain yield though studying water-saving irrigation techniques during the grain filling period. Using typical rice varieties as materials, this study investigated the effect of different irrigation regimes on grain yield and quality of rice and its physiological mechanism. The main results are as follows:1. A super rice variety Liangyoupeijiu was grown in cement tanks that were filled with soil. Two irrigation regimes, conventional irrigation (CI, continuous flooding) and alternate wetting and moderate soil drying (WMD, plants were re-watered when soil water potential reached-25kPa), were imposed form heading to maturity. The grain filling rate, the four key enzymes in sucrose-to-starch conversion, sucrose synthase (SuS, EC2.4.1.13), adenosine diphosphate-glucose pyrophosphorylase (AGP, EC2.7.7.27), starch synthase (StS, EC2.4.1.21) and starch branching enzyme (SBE, EC2.4.1.18) and abscisic acid (ABA) content of both superior and inferior spikelets were determined. The results showed that, when compared with the CI, the WMD significantly increased the grain filling rate, activities of SuS, AGP, StS and SBE and ABA content in inferior spikelets. The differences were not significant between CI and WMD regimes in grain filling rate, activities of the four key enzymes and ABA content of superior spikelets. Grain filling rate was very significantly and positively correlated with activities of SuS, AGP, StS and SBE. While ABA content was very significantly and positively correlated with activities of the four enzymes and grain filling rate. Application of ABA to plants at the early grain filling stage significantly increased ABA content, activities of the four enzymes and grain weight. Application of fluridone, an inhibitor of ABA synthesis, showed an opposite effect. The results suggest that a post-anthesis WMD could increase grain filling rate of inferior spikelets through regulating key enzymes involved in sucrose-to-starch conversion, and ABA plays an important role in this process.2. Two rice varieties of Yangdao6(indica) and Yangjing4038(japonica) were grown in both cement tanks and pots that were filled with soil. Three irrigation regimes, alternate wetting and moderate soil drying (WMD), alternate wetting and severe soil drying (WSD), and conventional irrigation (CI, continuous flooding), were conducted from heading to maturity. The effect of different irrigation regimes on grain yield and quality were investigated and its causes were analyzed. Compared with the CI, the WMD significantly increased filled-grain percentage, grain weight, brown rice rate, milled rice rate, head rice, gel consistency, peak viscosity and breakdown values, and significantly reduced chalky grains, chalky area, chalkiness degree, hot viscosity, final viscosity and setback values. The results were reversed under the WSD. The WMD also increased the albumin and glutelin content of milled rice, and decreased the prolamine content. The WSD increased the albumin content and decreased globulin content. The WMD significantly increased contents of the free-putrescine, free-spermidine, and free-spermine, and decreased ethylene evolution rate in grains. The WSD showed an opposite effect. The MWD significantly increased biomasses of shoots and roots, chlorophyll content of leaves (SAPD values), leaf photosynthetic rate, grain-leaf ratio and root oxidation power. The WSD had detrimental effects on shoot and root growth.Collectively, the results demonstrated that an alternate wetting and moderate soil drying during grain filling could increase grain yield and improve grain quality of rice. Increases in activities of key enzymes involved in sucrose-to-starch conversion and contents of ABA and polyamines and decreases in ethylene in grains, and harmonization in shoot and root growth would be important physiological bases for high grain yield and good quality under such an alternate wetting and moderate soil drying irrigation.