Effects Of Nitrogen Rate And Density On Grain Number Formation In Different Spike-Type Wheat Cultivars

Improving grain number is the target of ultra-high yield wheat cultivation and breeding, and grain number is the ultimate embodiment of floret differentiation, development and seed setting. The improve of grain number is a comprehensive reflection of varieties of morphological structure and physiological function, and grain number is regulated by the external ecological environment and cultural practices, nitrogen fertilizer and density are important ecological factors affect the formation of grain number. Therefore, difine the effect of nitrogen and density on morphology organs development, physiological basis and carbon and nitrogen substances metabolism during grain number formation process has an important realistic significance.In our study, we selected large panicle cultivar Lankaoaizao8, multi-panicle cultivar Yumai49and medium panicle cultivar Yangmai13. Split-plot design was employed in this experiment, the main treatment was nitrogen level including150kg-hm"2(N150)and225kg-hm-2(N225), the subplot treatment was density including150*104plant-hm"2(D150) and300*104plant-hm-2(D300). We analysed the effect of nitrogen and density on seed setting features, morphology organ building, photosynthetic characteristics, dry matter accumulation and translocation and the physiology basis of floret degradation, and initially defined the formation mechanism of wheat grain number and the regulation by cultural factors. The main results were as follow:1. Lankaoaizao8has significantly higher florets, fertile florets and grain number, high density inhibited the increase of spikelet number,and reduced the floret differentiation and grain setting, thus increase the degradation of florets; increase the nitrogen level contributes the formation and fertility of florets.. Grain number, and single grain weight in different spikelet positions showed parabolic changes, basal and central spikelet, proximal grains have optimal performance. Significant difference appears among wheat cultivars with different spikelet type. Lankaoaizao8with big spike has more grains and higher weight than other cultivars. Nitrogen significantly improves the grain numbers of basal spikelet, total grain numbers reduced with increasing density. Increased amount of nitrogen application inhibited the increase of grain weight (apart from the apical spikelet), distal grain is the most sensitive part to nitrogen; grain weight reduced when density is higher, and basal spikelet was affected the most.2. Increasing nitrogen will extend the period of spike differentiation and differentiation strength. Leaf length and width increased significantly with the increase of nitrogen, but increased density is not conducive to, leaf characters have close relationship with grain number.Lankaoaizao8has the highest dry matter accumulation in all organs, high nitrogen rate and increasing density is not conducive to leaf dry matter accumulation spike weight, stem weight and grain number has close relationship. With the growth period advancing, the ratio of panicle weight and stem weight gradually increases; if the nitrogen rate was higher, the ratio was higher, Yumai49has bigger ratio than other cultivars.3. Lankaoaizao8has the highest chlorophyll content within three cultivars from booting to anthesis stage; Yangmai13has the maximum efficiency of nitrogen effect. The net photosynthetic rate in top three leaves of Lankaoaizao8was the highest, the top second leaf has the highest net photosythetic rate at booting while at anthesis was the flag; increased nitrogen level extended the sustained period of high light efficiency, high density reduced the photosynthetic rate. Total soluble sugars and sucrose content presented first decreased and then gradually rising trend in Yumai49, the high nitrogen inhibits the synthesis and storage of sucrose in the flag leaf. From booting stage to anthesis, the nitrogen content in various parts downward trend. Lankaoaizao8has higher nitrogen content than other two cultivars. N content and change amount in ear stem and grain number were significantly correlated.In summary, the lower the density and high nitrogen fertilization is conducive to the differentiation and seed setting of florets, and minimize the degradation of the base and the top spikelet upper floret. At the same time extend the strength and time of the panicle differentiation, to promote the increase of leaf area and dry matter accumulation. Increase the photosynthetic rate of the2nd leaf at the booting stage and the flag leaf at anthesis, and promote the accumulation of carbon, a reasonable nitrogen application on regulating carbon and nitrogen ratio, which will help to maximize the grain number.