| Grain filling is a key growth period for yield formation in rice, and the assimilation of plant production after heading accounted for the most part of the yield. The development and filling of the grain also determine the grain yield and quality .After heading, the grains per panicle and the sink size of a single grain determined by genetic factors have been decided, while the growth of grain sink size is influenced greatly by environment, and the stress conditions during grain filling period have a direct effect on grain filling. With the serious situation of global warming, the high temperature stress has become a frequent phenomenon in rice production. The effect of the high temperature stress on yield formation and quality has become an important issue for high yield and good quality in rice production. In this study, different types of Japonica cultivars used as materials, the effect of high temperature in different grain filling periods on grain yield, grain quality and plant physiological characteristics, such as photosynthetic production, was studied. The main results were as follows:1. In most cases, the high temperature stress including day and night reduced the yield in all the varieties. The high-temperature stress during early grain filling period significantly decreased grain yield, and performed consistently between varieties and spikelet fertilizers, while the effect of high-temperature stress during middle and late grain filling periods on yield varied with varieties, Nongken57 showed a better resistance to the temperature stress. In most varieties, the high temperature stress during middle grain filling period has a greater effect on yield than that during late grain filling period. The effect of fertilizer treatment on high temperature stress was more complex, and it varied with stress treatment duration and varieties. The effect of high day temperature stress on yield among treatments varied greatly and and the effect of high night temperatures was more obvious.2. High temperature stress during early grain filling period led to significant reduction in 1000-grain weight, although the decline in varieties was different, but the trend was consistent. The effect of grain fertilizer level on high-temperature stress had a great variation among varieties. Filled-grain rate also showed a similar trend under high temperature stress conditions, 1000-grain weight and filled-grain rate in most varieties showed decline in the stress synergistic effect, resulting in significantly lower yield. A few varieties, such asYangjing4038, although 1000-grain weight was not significantly decreased, the sharp decrease in filled-grain rate also resulted in significant decrease in yields. The effect of high temperature stress during early grain filling period on 1000-grain weight and filled-grain rate in the upper, middle and lower parts of panicle was consistent; indicating it also had significantly adverse effects on grain growth during middle and late grain filling period.3. High temperature stress worsened rice milling quality significantly, especially high temperature stress during early grain filling period and high night temperature stress. The impact of early high-temperature stress on the lower part of grain also occurred. On the appearance quality of rice mainly existed during early high temperature stress, chalky kernel percentage increased sharply, chalky area was significantly larger, resulting in significant increase in chalkiness. The effect of medium-term high night temperature stress was greater than that of medium-term high temperature stress. Heat stress treatment in most varieties led to the increase in protein content, particularly high night temperature during early grain filling period. Under high temperature stress, amylase content and gelatinization temperature rose significantly at most treatments, especially high night temperature treatment had become more evident. In a word, the high temperature stress during grain filling period significantly reduced rice quality. This trend also had reflected by the characteristics of RVA4. High temperature stress during grain filling period reduced the single stem weight, but recovery phenomenon was found after the end of treatment. With the delay of high temperature, the panicle weight was reduced slightly, showing that the impact of high temperature on panicle weight was lager during the early period. Different from single stem weight, it had less ability to recover form the high temperature stress.5. The result of two consecutive years showed that the leaf SPAD values of rice under high temperature stress had an increasing tendency, and the levels of increase were different in the varieties. Monitoring of chlorophyll fluorescence showed that the Fv/Fm in the majority treatments under high temperature stress also increased significantly. In contrast, the photosynthetic rate under the high day temperature stress had no significant change and it reduced significantly under high night temperature stress condition. Under high temperature stress conditions, the MDA content of leaves had no obvious increase, but the significant accumulation of proline could be found. Early temperature stress led to the decrease in CAT activity, but the CAT activity increased significantly under the medium-term temperature stress. The POD activity increased under high temperature stress. The SOD activity in different varieties showed different changes, but it had not obvious regularity.6. Shading during different grain filling periods showed similar effects with high temperature stress. Shading treatment decreased 1000-grain weight and filled-grain rate, resulted in lower yield. The effect of early treatment was significantly higher than that of medium-term treatment and the stress during early grain filling period reduced grain weight in the middle and lower parts of panicle. The impact on rice quality was also similar with effect that of high temperature stress, indicating high temperature stress and low light intensity stress had some common characteristics. |
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