| In cold regkm, the practice in increasing panicles per unit land area and grains per panicle could not meet the need of yield increasing and quality improving in rice production in the future. More attention should be paid to increase the part of plump grains because blighted grain, i.e. poor grain-filled grain is the bar of yield increasing in rice production.Thirty-one cultivars/lines released in HLJ province were used in the studies. Studies by means of leaf cutting, spikelet thinning, fertilizer, as well as density treatments were carried out both in plot and pots in order to make sure the sink-source relation and how it plays the role in grain-filling regulation in cold-region rice. ?C02-label was also used in the studies. The results were summarized as follows:1.Difference of plump grain percentage between cultivars/liries was found. The plump grain percentage in cultivars with heavy panicle is higher than that of lightpanicle ones. And it is the same when comparing the cultivars of late maturity with the early ones.2.The grain-filling duration of cold-region rice could be fitted well with the Logic growth equation. The grains in early flowering were vigorous and both maximum and average grain-filling rates were high, earlier in reaching the maximum grain-filling peak, and only one peak appeared in the cure. On the opposite, the maximum and average grain-filling rates of the weak grain in late flowering were much lower, the highest grain-filling peak appeared late, and two peaks could be found in the same cure. It means that the grain-filling duration of grains on lower branches (the 2nd branches in the study) were regulated by the upper ones (the primary branches). The grain-filling rate became lower when the dry matter used in grain filling couldn抰 meet the need of highest grain-filling demand. All mentioned above implied that the entire duration of grain filling reflected the relationship between source and sink. And the shortage of dry matter supply in grain filling should be the key factor in blighted grain formation.3.In general, the green leaf area of rice in cold region was getting down gradually during the grain-filling period and then turned distinctly when the vigorous grain reaching the highest grain-filling peak. The rate of leaf area decreasing could be found between cultivars/lines. The rate of green leaf area decrease was negatively related to increase the well grain-filling grain percentage (PGP) and grain filling degree (GF). The relation between the ratios of leaf area to grain was negative and significantly three weeks after heading.4.The dry matter production and distribution were regulated by source-sink structure during grain filling. The amount of dry matter produced, assimilate distributed for each grain and transferred from culms and leaf sheath was different significantlybetween cultivars/lines, treatments of fertilizer level, as well as density. The result of ?C02-label indicted that 15 days after feeding with 14C02, the higher attenuation speed in flag leaf, the higher the PGP was. Twenty days after heading, the higherthe radiation account in grain, the higher the POP was.5. The PGP and GF improved significantly with the change of source-sink structure. Leaf cutting reduced the PGP and OF and spikelet thinning increased. As for rice plant in cold region, negative effect of leaf cutting on PGP was significant than the positive effect of spikelet thinning on POP. Different cultivars showed different responses to source-sink structure changes, and the compensation in rice plant could be found in the treatments of leaf cutting and spikelet thinning.6.Increasing nitrogen supply caused the decrease of POP. However, topdressing two weeks before heading increased the rates of dry matter production and accumulation during grain filling. Late nitrogen fertilizer increased the chlorophyll content of the upper functional leaves and delayed the senescence of the plant.7.Under the condition of transplantation in lower intensity, tillers of early maturity...
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