Effects Of Planting Density On Wheat Sugar-spikelet Ratio During The Flowering Stage And Grain Filling

Wheat grain yield is determined by spike number per unit area, grain number and grain weight per spike, spike number per unit area is regulated by planting density, which attributes to the forming of different wheat populations with different sugar-spikelet ratios(ratio of non-structural carbohydrates in stem and sheath and number of spikelet), generally speaking, sugar-spikelet ratio increased with the increment of planting density, which leaded to the decreasing of non-structural carbohydrates distributed to the grain and the reduction of grain weight, besides, grain number per spike was negatively correlated to planting density, grain weight was different according to its position on the spike, grain-filling rate of superior grains was faster than that of inferior grains whose florescence were later, but this kind of disparity was not unchangeable, according to the results of related studies concerning rice, the enhancing of sugar-spikelet ratio during florescence could increase grain-filling rate and grain weight of inferior grains, thus leading to the increment of grain yield. Studies concerning the relationships between grain-filling rate of wheat superior/ inferior grains and sugar-spikelet ratios were not common seen, as it was very important to figure out the proper sugar-spikelet ratio in order to enhance grain weight of inferior grains, Xinong979 and Xiaoyan22 were chosen as testing materials in this study, different planting densities were set to create different wheat populations with different sugar-spikelet ratios, through the measuring of grain-filling parameters of superior/ inferior grains, the contents of endogenous hormones and activities of related antioxidant enzymes, it could be concluded that:(1) Planting density played an important role in the growing and grain-forming process of wheat, number of tillers per unit area increased with the increasing of density, while number of tillers per plant showed an opposite trend. As for the amounts of dry matter accumulation, no significant differences were found from 3-leaf stage to jointing stage, while a negative correlation between dry matter accumulation and planting density were observed. Grain yield of Xinong979 performed better than Xiaoyan22, and when they both reached their highest value, the density of Xinong979 was higher, which illustrated that Xinong979 was more density-resistant.(2) A negative correlation between sugar-spikelet ratio and wheat planting density was observed, during heading stage, the content of non-structural carbohydrates(NSC) in stemand the number of spikelet were both higher under high sugar-spikelet ratio condition, besides, the content of non-structural carbohydrates(NSC) in superior grains was also higher than that of inferior grains. NSC played an role in the process of early grain-filling stage, and the content of NSC was positively correlated to grain-filling intensity, this was one of the reasons that resulted to the worse performance of inferior grains. Grain-filling process of superior grains was generally not infected by sugar-spikelet ratio, while the grain-filling process of inferior grains was greatly influenced by sugar-spikelet ratio. Grain-filling rate of Xinong979 was significantly higher than that of Xiaoyan22, and its showing time of maximum rate was earlier, no significant difference of grain weight was observed in the end, that might be due to the longer grain-filling process of Xiaoyan22 compared to Xinong979.(3) The worse performance of inferior grains was also owing to the low contents of promoting hormones such as, abscisic acid(ABA), auxin(IAA) and zeatin riboside(Z + ZR), the contents of promoting hormones were all positively correlative to sugar-spikelet ratio and showed a first increase-then decrease single peak curve, which was in accordance with the changing trend of grain-filling rate. However, the content of inhibitory hormone, such as gibberellin(GAs) decreased all the time and was negatively correlated to sugar-spikelet ratio. By testing the activities of antioxidant enzymes in wheat flag leaves, it could be inferred that activities of promoting hormones were all positively correlative to sugar-spikelet ratio, among which SOD activity and POD activity first increased then decreased, while CAT activity decreased all the time; Inhibitory hormone(MDA) activity increased all the time and was negatively correlated to sugar-spikelet ratio. All in all, the grain-filling process of Xiaoyan22 was more susceptible to sugar-spikelet ratio than that of Xinong979.