| Improvement in rice quality is an important target in the production, and grain-filling is the most important stage of the rice quality. This study was designed to elucidate the humidity management technique improved the formation of rice quality during grain filling. Typical Indica and Japonica were used as materials, and tank-grown, pot and field experiments were conducted. Treatments of dry-wet alternate irrigation and different N levels during the grain filling period were designed for each experiment. Effect of dry-wet alternate irrigation and N levels on rice yield, quality and their mechanism were investigated. The main results are as follows:1. Well-watered (control), moderate dry-wet alternate irrigation (soil was re-watered when soil water potential reached at–25 kPa), and severe dry-wet alternate irrigation (soil was re-watered when soil water potential reached at–50 kPa) were imposed from heading to maturity in cement tank and paddy field. Compared with the control, the moderate dry-wet alternate irrigation increased filled-grain percentage and grain weight, improved the milling quality, and reduced chalky kernels and chalkiness. It also increased peak viscosity and breakdown values and decreased hot viscosity, final viscosity and setback values. The results were reversed for the severe dry-wet alternate irrigation. The moderate dry-wet alternate irrigation closed amyloplast arrangement in the grain belly, and the severe dry-wet alternate irrigation loosened amyloplast arrangement and reduced the size of amyloplast.2. Activities of sucrose synthase (SuS), adenine diphosphoglucose pyrophosphorylase (AGP), starch synthase (StS) and starch branching enzyme (SBE) in the grains were significantly enhanced by the moderate dry-wet alternate irrigation, but reduced by the severe dry-wet alternate irrigation. No significant difference in acid invertase (AIV) activities in the grains was observed among the treatments. Activities of SuS, AGP, StS, and SBE were significantly and positively correlated with grain weight, peak viscosity, and breakdown values, whereas significantly and negatively correlated with chalkiness and setback values.3. Compared with the control, the moderate dry-wet alternate irrigation significantly increased the Concentrations of zeatin (Z) + zeatin riboside (ZR) in roots, the root oxidation ability and NR activities, and increased the photosynthetic rate of the flag leaves. It also increased the rice endosperm cells of inferior grains and significantly induced ethylene evolution and ACC concentration. The results were reversed for the severe dry-wet alternate irrigation.4. The strength of the effects of spikelet fertilizer on grain yield and quality of rice depended on the different irrigated mode in pot experiment. Under well-watered condition, compared with 0N (no N), MN (two g per pot) and HN (four g per pot) significantly increased grain weight, improved the milling quality, chalky kernels and chalkiness. It also increased gel consistency and setback values, and decreased peak viscosity and breakdown values. Under the moderate dry-wet alternate irrigation, MN significantly increased filled-grain percentage, grain weight, peak viscosity and breakdown values, improved the milling quality, and reduced chalky kernels, chalkiness and setback values; HN increased grain weight, improved the milling and cooking qualities. Under the severe dry-wet alternate irrigation, MN and HN significantly increased chalky kernels, chalkiness and setback values, and decreased peak viscosity and breakdown values, but little affected grain yield. MN and HN all enhanced gel consistency, increased protein content and decreased amylase content under three irrigated modes.5. Different irrigated modes and N levels during grain filling significantly affected the components of protein of rice grain. Compared with the well-watered, the moderate dry-wet alternate irrigation increased the albumin and glutelin content of milled rice, decreased the prolamine content; the severe dry-wet alternate irrigation increased the albumin content, and decreased globulin content. The components of protein of milled rice were increased with the increase of N levels under three irrigated modes.The results suggest that the moderate dry-wet alternate irrigation during grain filling can increase rice grain yield, optimize the structure of endosperm, improve the milling, appearance and cooking qualities of rice. Under the moderate dry-wet alternate irrigation, the increase of cytokimin concentrations in roots, the reduction of ethylene concentrations and the enhancement of SuS,AGP,StS and SBE activities contribute to the increase of grain yield and improvement of rice quality. Moderate dry-wet alternate irrigation with a certain level of N promotes increasing grain yield and improving rice quality. |
