Effects Of Seeding Rate On Yield In Wheat Cultivars From Different Eras And Its Physiological Basis

Wheat is an important food crop worldwide. Genetic improvement is an improvement way in wheat grain yield enhancement. It is great significance for the food security in our country and even the world. It has an important role to improve grain yield with reasonable group structure, and seeding rate is basic factor to determine the group structure. Elucidating the evolution characteristics and suitable group of high grain yield in wheat cultivars from different eras would be favor of determining guiding cultivar breeding objective and rational cultivation measures for high yield in the future. Field experiment were conducted using thirty-three winter wheat (Tritieum aeslivum) cultivars released from1950s to2000s to investigate the effects of seeding rate on grain yield, group structure, photosynthetic produce characteristics and nitrogen uptake and utilization. The main results were as follows:1. The effects of seeding rates (120,180and240×104seeds hm-2) on grain yield formation of wheat cultivars from different ears with two nitrogen levels of0and225kg/hm2were investigated. The results showed that there were significant differences in grain yield and yield components among thirty-two cultivars and seeding rate. The grain yield, kernels per spike,1000-kernel weight, spikelet fertility, dry matter accumulation from emergence to jointing and anthesis to maturity of the2000s’cultivars were higher than those of old cultivars (1950s,1960s,1970s,1980s,1990s), but spikes per hm2, spike length, spikelet number and dry matter accumulation from jointing to anthesis were lower. Along with the increase of density, spikes per hm2of wheat cultivars from different ears were increased; moreover, the rate of fertile tillers, kernels per spiked,1000-kernel weight, spike length, spikelet number and spikelet fertility were decline; grain yield and dry matter accumulation of2000s’cultivars were increased and1950s’cultivars were declined, which indicated maintaining coordinating the relationship of spike traits and dry matter accumulation with increasing seeding rate is beneficial to improve grain yield of modern cultivars.2. The effects of seeding rates (120,180,240and300×104seeds hm-2) on group structure of wheat cultivars from different ears were investigated. The results showed that there were significant differences in group structure and photosynthetic capacity among cultivars and seeding rate. The LAI, dry mater accumulation and photosynthetic capacity of the2000s’ cultivar were higher than those of old cultivar under each seeding rate, but population culms were lower. Along with the increase of density, group quality targets and photosynthetic capacity in late filling of the2000s’ cultivar were increased, but the rate of fertile tillers was declined. The correlation analysis showed that grain yield were significantly positively correlated with LAI and dry mater accumulation, but negativly with population culms, which indicated maintaining the2000s’ cultivar has strong automatic adjustment ability, in older to create a reasonable and effective growth condition, and improve group quality, it should be appropriately increased seeding rate and control the middle growth, then gets the best combination of spikes per hm2, kernels per spike and1000-kernel weight, so as to realize the ideal and higher yield group stable.3. The effects of seeding rates (120,180,240and300×104seeds hm-2) on nitrogen uptake and utilization of wheat cultivars from different ears were investigated. The results showed that nitrogen transfer capacity, nitrogen utilization efficiency, NR and GS activity of flag leaf of2000s’ cultivar were significant higher than those of1950s’ cultivar under each seeding rate. With increasing of seeding rate, the nitrogen transfer capacity of vegetative organs of modern cultivar was significantly declined, but the older cultivar’s was increased; NRE and NAE of wheat cultivars from different ears were significantly increased, but NHI was declined; NR and GS activity of flag leaf of modern cultivar were increased, but old cultivar’s were significantly declined, which indicated maintaining it is useful to improved nitrogen utilization efficiency and nitrogen metabolism ability of modern cultivar with appropriately increasing of seeding rate in the same soil condition.In summary, the2000s’ cultivars responses to seeding rate enhanced, and have the highest grain yield in240×104seeds hm"2, and the1950s’cultivars have the highest grain yield in180×104seeds hm-2. The better automatic adjustment ability of group in the2000s’ cultivars can enhance the plant photosynthesis production and nitrogen accumulation, distribution and use, so as to be favor of facilitating the formation of grain yield, and laying a foundation for the higher grain yield.