Regulatory Effects Of Delayed Sowing On The Grain Number,Weight And Protein Content At Various Positions Of Spikes For Different Wheat Cultivars

In wheat production in the Huang-Huai-Hai area,the delayed harvest of previous crops,insufficient moisture,or excessive rainfall often lead to delayed wheat sowing.Previous studies have shown that appropriately delaying the sowing date can increase or stabilize wheat grain yield by increasing the number of grains per spike,and at the same time improve its nitrogen utilization efficiency,but reduce its grain protein concentration.However,there are few reports on the regulatory effects of delayed sowing on the number of grains,grain weight and protein concentration at different position within a spike of different winter wheat cultivars.This study was carried out to further clarify the changes of grain composition and protein concentration of different wheat cultivars under delayed sowing conditions and to provide a theoretical basis for the coordination of quality and quality of delayed sowing wheat.The study was conducted in the experimental field of Dongwu Village,Dawenkou Town,Tai’an City,Shandong Province,for two consecutive wheat growing seasons,2019-2020 and2020-2021.Shannong 30,a large spike type winter wheat cultivar,and Luyuan 502,a multi-spike type winter wheat cultivar,were selected as test materials.Two sowing dates were set on October 8（suitable sowing date）and October 22（delayed sowing date）.The regulation effect of delayed sowing date on yield components,nitrogen accumulation and distribution of winter wheat cultivars with different spike types was studied.The main research results are as follows:1.Effects of delayed sowing date on yield components of different winter wheat cultivarsDelaying sowing date significantly decreased spike number per unit area but increased spike number of both cultivars.The 1000-grain weight of Shannong 30,a large spike type cultivar,did not change due to the delay of sowing date,while the 1000-grain weight of Luyuan 502,a multi-spike type cultivar,decreased significantly due to the delayed sowing date.The grain weight per spike of both cultivars increased significantly due to the increase of grain number per spike after delayed sowing date.Due to the decrease of spike number per unit area and the increase of spike number caused by delayed sowing date,the spike number per unit area of Shannong 30 increased,while the spike number of Luyuan 502 remained unchanged.Results the grain yield of Shannong 30 increased in two growing seasons,Luyuan502 decreased in 2019-2020 growing season and remained in 2020-2021 growing season.In conclusion,whether the increase of spike number can make up for the decrease of spike number per unit area and/or grain weight is the key factor that determines the increase or decrease of yield under the delayed sowing condition.The delayed sowing dates resulted in the decrease of tillers and the decrease of total tiller number per unit area in each growth period,but the tiller heading rate increased.The population size of the multi-spike cultivar Luyuan 502 was more sensitive to the delayed sowing date.Compared with the two cultivars,the number of tillering tillers before winter,the maximum number of tillering tillers in spring and dry matter weight per tiller decreased less than Luyuan 502,but increased more than Luyuan 502.2.Effects of delayed sowing date on grain number（weight）composition in different position within a spike of different winter wheat cultivarsThe number of grains per spike was significantly increased,and the increase of the top spike was significantly greater than that of the base section and central section of a spike as affected bydelayed sowing date.With the delayed sowing dates,the inferior grains increased significantly at each spike of the two cultivars,and the increase rate was the highest at the central section,the lowest at the apical section of a spike.As for the superior grain number,Shannong 30 only increased significantly at the apical section of a spike,but remained unchanged at the basel and central section of a spike.The performance of Luyuan 502 was different between seasons.In general,with the delay of sowing date,the proportion of spike number at the apical section of a spike to the total number per spike increased significantly,while the proportion of spike number at the basel and central section of a spike decreased significantly.Grain weight of spike and the grain weight of superior and inferior grain of Shannong 30remained unchanged as affected bydelayed sowing date in two growing seasons.The average grain weight at the central section and the apical section of a spike for Luyuan 502 decreased significantly,while the average grain weight at the basel section showed different performance between seasons.As for the superior and inferior grains,the superior grain weight at the basel and central section decreased significantly after delayed sowing,while the superior grain weight at the apical section of a spike had no significant change.The average grain weight of the superior grain in the whole spike of Luyuan 502 decreased significantly in the two growing seasons,while the average grain weight of the inferior grain was different from season to season,and the average grain weight of the inferior grain decreased significantly in the 2019-2020 growing season.The 2020-2021 growing season remains unchanged.3.Effects of delayed sowing date on the production and distribution of ¹³C assimilates during spike and flower development of different cultivarsFrom the differentiation stage of florets primordium（W3.5）to the formation stage of septum（W7.0）,the assimilation capacity of ¹³C per shoot of both cultivars was significantly improved.Although the assimilation capacity of ¹³C per shoot of late sowing in early spike development stage was lower than that of suitable sowing stage,the increase rate of late sowing treatment was significantly higher than that of normal sowing treatment due to the advance of the development process of spike.The assimilation amount of ¹³C per shoot in late sowing was significantly higher than that in normal sowing.At anthesis,the accumulation and distribution ratio of ¹³C isocompounds marked at the three stages of spike differentiation were significantly increased due to the delay of sowing date,but the accumulation and distribution ratio of ¹³C isocompounds in stem decreased correspondingly.At maturity stage,the accumulation amount and distribution proportion of¹³C assimilates in spike marked by the above three stages also increased significantly,while the amount and distribution proportion of ¹³C assimilates in stem and leaves decreased significantly.Compared with the three section of spike,the increase of apical section of a spike was higher than that of basel and central section.With delayed sowing,the allocation ratio of ¹³C assimilates to both superior and inferior grains of Shannong 30 increased significantly,and the allocation ratio of inferior grains increased more,but no such difference was observed between superior and inferior grains of Luyuan 502.The increase of assimilates produced during the development of spike and flowers after delayed sowing provided a more sufficient material guarantee for the development of spike flowers under delayed sowing,especially for the fruiting of apical section of spikes and the fruiting of inferior grains.4.Effects of delayed sowing date on post-anthesis photosynthetic characteristics and ¹³C assimilate allocation of different cultivarsThe delayed sowing had no significant effect on the canopy light interception of the two cultivars,but significantly increased the flag leaf SPAD,flag leaf maximum net photosynthetic rate,population photosynthetic rate and population photosynthetic high duration of the two cultivars,and the increase of Shannong 30 was significantly higher than that of Luyuan 502.According to the dynamic changes of photosynthetic rate of flag leaves after anthesis,the photosynthetic rate of flag leaves under late sowing of Luyuan 502 was always higher than that under suitable sowing period,while the photosynthetic rate of flag leaves under late sowing of Shannong 30 mainly showed a longer duration in late filling period.After delaying the sowing date,the population net photosynthetic rate of the two cultivars increased significantly,and the increase rate of Shannong 30 was significantly higher than that of Luyuan 502,and the high-value photosynthetic duration was also significantly extended.The increase in dry matter production capacity and the allocation of assimilates to each position within a spike after late sowing was conducive to the increase in total grain weight of the basal,central and apical positions and the total grain weight of superior and inferior grains of a spike.However,the trade-off between the amount of photosynthetic assimilates allocated to the grains and the increase in the number of grains set differed among cultivars:for Shannong 30,the increase in the weight of grains set at each spike was basically the same as the increase in the number of grains set under late sowing,so the weight of grains set at each spike remained stable and the average weight of grains per spike was unchanged;for Luyuan502,the assimilates allocated to the central and apical section of spikes under late sowing were not sufficient to offset the increase in the number of grains set.For Luyuan 502,the assimilates allocated to the central and apical section of spikes were not sufficient to offset the increase in the number of fruiting grains,resulting in a decrease in grain weight and thus a significant decrease in the average grain weight.5.Effect of delayed sowing on the protein concentration of grains in different sections of the spike of winter wheat varietiesAfter the delayed sowing,the grain protein concentration of each spike of both cultivars decreased significantly,and showed a decreasing trend from the base to the top of the spike.The grain protein concentration of both superior and inferior grains of both cultivars decreased with delayed sowing,but the decrease was greater for inferior grains.Compared with the changes in grain weight and grain yield per unit area,the deficiency of nitrogen allocation to each spike and the deficiency of total grain nitrogen accumulation per unit area at maturity under late sowing was the main reason for the decrease in grain protein concentration at each spike and average grain protein concentration per unit area,both of which were mainly related to the decrease in total aboveground nitrogen accumulation and nitrogen uptake efficiency after late sowing.That were mainly related to the decrease in total aboveground nitrogen accumulation and nitrogen uptake efficiency after late sowing.The nitrogen content of individual grains of Luyuan 502 decreased significantly with delayed sowing,while that of Shannong 30 did not change significantly.The total nitrogen content of grains at the basel of the spike of both cultivars decreased significantly,but there was no significant change in the other two sections.Nitrogen accumulation in grains of both cultivars,N accumulation in apical section grains and its proportion to N accumulation in whole spike increased significantly with delayed sowing.The proportion of nitrogen accumulation of superior grains in total grains nitrogen accumulation was significantly lower in both cultivars,and the proportion of nitrogen accumulation of inferior grains was significantly higher.