| Rice is one of the important crops that feed more than 65% of population in China. Enhancing the rice production in per hectare is an effective approach to ensure the grain security, as the arable area is reducing in China. Because of the super rice program, high-yielding rice cultivars were reported frequently, i.e. super rice Yongyou12. However, those super rice cultivars with large panicle including Yongyou12 often fail to achieve the high yield potential mainly ascribed to the lower seed-setting rate. Therefore, it is necessary to analyze the physiological characteristics of high-yielding rice cultivars. The results can provide references to the researches of cultivation techniques for those super rice cultivars. A great number of researches have been conducted on the physiological characteristics of high-yield rice cultivars with Yongyou12, whereas considerable attention has focus on its population characteristics and plant morphology. Rather less consideration has been given to the characteristics of assimilate translocation of Yongyou12. Therefore, two super rice cultivars, Yongyou12 and Yongyou9 were selected in this experiment to reveal the mechanism underlying the higher assimilate translocation showed in the former than the latter. According to this finding, the effect of plant growth regulators including GA and 3.2% GA3·PP333(LLB) on the grain yield of Yongyou12 were also discussed. The results were followed:1. To investigate the physiological characteristics of super-high-yielding rice variety, two cultivars Yongyou-9(control) and Yongyou-12(super high-yielding variety) were field grown. The dry matter accumulation, photosynthetic rate, dynamic changes of gain filling, soluble carbohydrate, N, P and K of plant organs, gene expression of sucrose transporter and the quantity and size of vascular bundle were determined and observed. The result showed that the grain yield of Yongyou-12 was significantly increased by 13.8%~17.6% when compared with the control. As to the yield components, the effective panicle numbers, seed-setting rate and 1000-grain weight were significantly decreased, while the grain numbers per panicle was significantly increased as high as 41.1%~51.8% comparing to the control. The difference in nutrient elements of N, P and K in plant organs between Yongyou-9 and Yongyou-12 was not significant, while grain filling rate and grain weight of superior and inferior spikelets in Yongyou-12 were significantly decreased. When compared with the control, the super high-yielding variety Yongyou-12 had the advantage in higher net photosynthetic rate during the early grain filling stage, more dry matter accumulation during the whole growing period, higher gene expression of OsSUT1, OsSUT2 and CIN2, vascular bundle numbers and soluble carbohydrate in grains, which indicating a higher efficiency in delivering assimilate from leaf to grain. It indicated that the physiological bases of super-high-yielding cultivar Yongyou-12 attributed to its high accumulation and transformation of assimilates. It is important for high-yielding breeding and cultivation to promote transformation efficiency in rice varieties, and to increase grain yield and make existing resources more efficient.2. The difference in seed setting rate of superior grains between Yongyou12 and Yongyou9 was not significant, while that of inferior grains was significantly lower in Yongyou12 than Yongyou9. For Yongyou12, the seed setting rate of superior grains was 19% and 52% higher than that of inferior grains in 2013 and 2014, while it was 6% and 13% in Yongyou9. The difference in seed setting rate between superior grains and inferior grains of the two cultivars might closely related to their numbers and germination rate of stigma pollen grains. The stigma pollen grain numbers of superior grains were significantly higher than inferior grains in both cultivars, and especially for Yongyou12. However, the stigma pollen grain numbers were more than twenty, which indicated that reproductive barriers did not exist. The germination of pollen grain was hardly observed on stigma in Yongyou12. The distribution of photosynthetic product would be the main limited factor. The photosynthetic rate of flag leaf determined when at anthesis of superior grains or inferior grains and it changed little. However, the soluble carbohydrate in superior grains was significantly higher than inferior grains. The distribution of assimilates were further related with the content of GA3 and ABA for their consistency in change tendency.3. GA reduced the tiller numbers and controlled invalid tillers of Yongyou12 and Yongyou9 when spraying in the effective tillering stage, while high concentration would reversely reduce the panicle numbers. The plant height, specific leaf weight, single stem weight under GA treatments was significantly higher than the control, and the increment effect improved with concentration of GA. However, the grain yield did not increase correspondingly. The grain yield of Yongyou12 under GA treatment was significantly decreased, while low concentration of GA increased grain yield of Yongyou9. The actual grain yield under GA treatment with the concentration of 10 ppm and 20 ppm was 13.07% and 5.65% higher than the control. Furthermore, GA treatment enhanced the logging resistance of Yongyou9. The author observed that the stem of Yongyou9 in the control was broken, while it was reversed in GA treatments. GA enhanced lodging resistance of Yongyou9 by increasing dry matter accumulation, thickness and pole substantial degree of stem.4. Rice plants of Yongyou12 sprayed with 3.2% GA3·PP333(LLB) at 3 days after heading increase the grain yield to some extent. This may ascribe to the improvement in seed-setting rate and kernel weight of LLB treatment compared with those of the control. There is no significant difference in pollen viability and pollen numbers on stigma between the LLB treatment and control, while the LLB treatment significantly increase the pollen germination on stigma, which is responsible for the improvement in seed-setting rate. Additionally, the chlorophyll content, net photosynthetic rate and specific leaf weight of flag leaf in the LLB treatment are higher, while the ratios of soluble sugar content in leaf and grain is lower than those of the control in the late grain filling period, indicating that LLB not only delay the leaf senescence but also promote transportation of assimilates to grains. |
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