Effect Of Plant Density On Floret Development And Grain Setting Characteristics Of Winter Wheat

The number of grains per spike is one of the main components to determine the yield of winter wheat.Investigate the influence of planting density on floret development and grain setting characteristic was important to realize high-yield and efficient cultivation of wheat.A two-factor split field experiment was conducted during 2020～2022 winter wheat seasons.Hengguan 35(HG35)and Jimai 22(JM22)were used as the experimental materials.Four densities were set for each cultivar,which were 180×104(D180),300×104(D300),420 × 104(D420),540 × 104(D540)plants·hm-2.In this experiment,the effects of density on floret development,spatial distribution characteristics of kernel number and weight of main stem and tillers were studied.The effects of density on the main stem and tillers production capacity of winter wheat were also clarified.The results would provide theoretical basis for high-yield and high-efficiency cultivation of wheat.The main results were summarized as follows:1.Reducing plant density promoted floret development,reduced floret degradation,and increased florets setting rate.For D180,the F4(F1,F2,F3,F4 depending on the particular spikelet position,from the most proximal(F1)to the most distal(F4)position with respect to the rachis)at the 9th spikelet in the middle position of the spike of the two cultivars and the F3 at the 17th spikelets in the upper position of the spike of HG35 developed to W9.5-W10 and therefore,to be fertile floret.While,for D540,the florets in the same spikelets position only developed to W6-W8,and finally degenerated.The florets setting rate of HG35 and JM22 in main stem under D180 was 24.24%and 12.12%higher than that under D540,the values were 49.96%and 50.38%in Ⅰ tillers,the values were 54.92%and 43.36%in Ⅱ tillers,respectively.The florets setting rate decreased obviously with the increased of tiller position,reducing density is beneficial to increase florets setting rate.2.Plant density significantly affected grain numbers per spike.The kernel numbers of each treatment increased at first and then decreased with the increase of spikelet position.Reducing density could effectively promote the grain setting of fertile florets in the upper spikelets of the main stem and Ⅰ and Ⅱ tillers,inferior florets in the middle spikelets of Ⅰ andⅡ tillers.The kernel numbers of HG35 and JM22 in main stem under D180 was 26.01%～28.07%and 19.40%～21.26%higher than that under D540,the values were 36.95%～50.59%and 24.01%～58.84%in Ⅰ tillers,the values were 68.24%～104.92%and 45.81%～50.40%in Ⅱ tillers,respectively.The kernel numbers decreased obviously with the increased of tiller position,reducing density is beneficial to increase grain numbers.3.Density has no significant effect on yield single kernel weight.The single grain weight of each treatment increased at first and then decreased with the increase of spikelet position,and the single grain weight of different floret positions ranked in F1,F2>F3>F4.Decreasing density increased the single grain weight of superior florets in the middle and upper spikelets of Ⅱ tillers of JM22.While the contribution of those grain weight to total grain weight was small due to the lower proportion of Ⅱ and Ⅲ tillers to the number of spikes at maturity stage.There was no significant different in single kernel weight between densities.The increase of grain number was the main reason for the increase of spike weight in low density.4.Density has no significant effect on yield.Across the four densities in the two seasons,the grain yield ranged from 9412.01 to 10443.38 kg·hm-2.Low density significantly increased the kernel numbers per spike and the percentage of effective tillers.The tillers yield accounted for 64.85%～66.67%and 46.93%～47.16%of the total yield in D180 and D300,respectively.While,the main stem yield accounted for 66.39%～66.46%and 79.10%～79.26%of total yield in D420 and D540 treatments,respectively.In conclusion,in this experiment,the yield of winter wheat could reach to 9000 kg·hm2 under the four plant densities.Low density increased the dry matter accumulation in spike,reduced floret degradation and promote the grain setting of fertile florets in the upper spikelets of the main stem and I and II tillers,inferior florets in the middle spikelets of I and II tillers.Reducing density also improved the percentage of effective tillers,then achieved high yield.On the contrary,high density reduced spike numbers,but increased the main stem productivity by increasing the proportion of main stem to spikes,and achieved higher yield.