Mechanism And Ways Of Improving Grain Weight In Rice (Oryza Sativa L.)

Field and pot and dydroponical experiments were carried out in Yangzhou university in 1999 ~ 2002 with different varieties as materials including typical indica, japonica and hybrid indica. With a large numbers of treatments for changing nutritious level of plant during hull formation stage, effects of that on hull growth and development were studied. And with a large numbers of treatments for changing levels of available grain filling substances in the filling stage, effects of that on grain plumpness were studied. These experiments were supposed to illuminate the mechanism and ways of improving grain weight in rice. Main results obtained were as follows:1. 1000-grain weight of every varieties varied significantly under different cultural and environmental conditions. The 1000-grain weight ranged 6.69g under different cultural and environmental conditions in Yangdao 6, 7.52g in Nipponbare, 3.79g in Wuyunging 8, 5.85g in Shanyou 63. The ratio of the maximal grain weight to the minimum grain weight was 1.28 in Yangdao 6, 1.38 in Nipponbare, 1.15 in Wuyunging 8, 1.25 in Shanyou 63; 1000-grain weight of the different specific gravities ranged 4.34g in Yanging 2, 8.89g in Yangdao 4, 7.40g in Shanyou 63, 10.76g in 02428/Minghui 63. The ratio of the maximal grain weight to the minimum grain weight of the different specific gravities was 1.22 in Yanging 2, 1.41 in Yangdao 4, 1.31 in Shanyou 63 and 1.54 in 02428/Minghui 63.2. Reducing N application concentration from transplanting to heading properly or employing feasible amounts of tiller promoting fertilizer would result in obvious increment of hull area and grain weight. While raising N application concentration fromtransplanting to heading or employing excessive spike fertilizer would result in obvious decrement of hull area and grain weight. Employing feasible amount of top dressing at heading would be beneficial to grain weight increment. Compared with CK, Shading and water stress treatments during hull formation stage or root-cutting treatment on the 15th days before heading would result in obvious decrement of hull area, grain plumpness and grain weight. Sand-adding treatment for promoting root growth would redound to hull area, grain plumpness and grain weight significantly. Effects of soil bulk density on hull area and grain plumpness and grain weight were subjected to the varieties. Optimum soil bulk density was 1.30g cm-3 for Nipponbare, 1.45g cm-3 for Yangdao 6.3. Increasing hull length and hull width could raising grain filling rate at early stage, promote growth of brown rice, and that would result in obvious increment of brown rice volume and grain weight. Increasing hull weight per unit hull area would raise grain plumpness and grain weight significantly. The variation of grain weight under different cultural and environmental treatments was essentially determined by the hull size, and that of grain weight among different specific gravities was essentially determined by grain plumpness, that were found to be consistent in the four varieties.4. The dynamic changes of hull length and width could be described with the Richards equation in Yangdao 6. In general, the maximum rate of hull growth were reached on the 10th~14th days before heading. The increment of hull width was a little slower than that of hull length. Ultimate length and width of hull were mainly subjected to hull growth rate during the main growth period(V2) and maximum hull growth rate(Vm). Reducing nitrogen content of plant properly and increasing content of soluble and insoluble carbohydrates of the plant during hull formation stage by feasible cultural conditions could increase hull length and hull width significantly.5. Raising dry matter accumulation and hull weight per unit hull area would result in the increment of grain plumpness, that was found to be consistent in the four varieties. Patterns of hull weight increment of strong and weak potential spikelets were quite different. For the hull of strong potential spikelets(SPSs), its weight increased very qu...