Differences In Grain Yield And Protein Content Between Main Stem And Tillers Of Strong Gluten Wheat And Their Responses To Nitrogen Application And Planting Densities

Wheat is an important ration crop and a strategic grain reserve variety in China.With the development of society and the improvement of people’s living standards,people’s demand for wheat yield and quality has also increased.China’s national conditions determine that wheat production must take into account the simultaneous improvement and coordinated development of yield and quality.In recent years,in order to meet social needs,the planting area of high-quality wheat has been expanded year by year,but there is a phenomenon that the yield and quality are not stable enough among different locations or years,resulting in the inability to balance the yield and quality.Appropriate cultivation measures can compensate for the adverse effects of production environment on wheat growth,promote the development of yield and quality balance,and improve its stability.The yield and quality of wheat are mainly determined by the composition of the stem and tiller in the group and the quality of the single grain.The balanced stem,tiller and grain of the individual characters are the basis for the synergistic improvement of yield and quality.Therefore,by studying the growth differences between wheat stems and tillers and between grain positions,cultivating stems and grains that can ensure a balance of quantity and quality,forming high-quality individual plants and groups,can achieve synergistic improvement and development of wheat yield and quality.This experiment was carried out at the Beijing Experimental Base of the Institute of Crop Science,Chinese Academy of Agricultural Sciences from 2019 to 2021 growth season.High-quality strong-gluten wheat was used as the test material,and the planting density and nitrogen application rate,which had a greater impact on wheat yield and quality,were selected as control measures.The experiment adopts a split-plot design,with three nitrogen application levels of 0kg hm^-2（N₀）,120 kg hm^-2（N₁）and 240 kg hm^-2（N₂）in the main plot,and 3 planting densities of 1.8 million hm-2（D₁）,2.7 million hm^-2（D₂）,3.6 million hm^-2（D₃）in the sub-plot,the varieties are sub-sub-plot:Shiluan 02-1（C₁）and Taishan 27（C₂）.The focus is on the effects of stem and tiller growth and agronomic traits,population composition and yield contribution per stem,dry matter accumulation and nitrogen content,strong and weak grain protein content and quality on wheat under the control of different nitrogen application rates coupled with cultivation density.The differences in the contribution of different tillers and grain positions to grain yield and quality were compared,and the physiological mechanism of the differences was analyzed from the perspectives of changes in tiller hormones,photosynthetic performance of leaves,and activities of nitrogen-metabolizing enzymes in grains.Provide technical support for the rational dense planting and application of nitrogen fertilizer for high-quality and high-yield of strong gluten wheat,and provide theoretical reference for its high-quality and high-efficiency cultivation research.The main results are as follows:1.Stem and tiller regulation mechanism of nitrogen fertilizer and density affecting wheat yield formationStudies have shown that wheat yield is weighted by the main stem and tiller yield（ear grain weight）,and the relationship between each stem and tiller yield and the total yield is:Y=A×∑[T_i×P_i]×G,where Y is Yield,A is the number of basic seedlings,Ti is the probability of tillering of each stem into panicles,Pi is the proportion of the total panicles of each stem to the total number of panicles,G is the grain weight per panicle,and i is the tiller position of each panicle（main stem,1N,2N...）.The high yield of Shiluan 02-1 is mainly composed of main stem,1N and 2N,and the main stem contributes 30%-45%,1N contributes 25%-35%,2N is about 15%-20%,the rest consists of 1N-1 and 3N.Under the high-yield condition of Taishan27,the main stem and 1N with similar contributions are the main components of yield,accounting for 40%-50%.Both 3N and 1N-1 of the two cultivars have great controllability and are buffer pools composed of high-yield populations,and their yield potential can be tapped through cultivation measures.2.Regulatory effects of dry matter accumulation and nitrogen content on wheat stem and tiller formationThe jointing stage is an important growth period for the polarization of wheat tillers.The results show that the dry matter accumulation and nitrogen content in the tillers before and after jointing have a high correlation with the ear formation rate,which can reflect the tiller formation to a certain extent.When the ratio of tiller to main stem dry matter exceeds 0.5,there is a 60%probability of forming an ear;the nitrogen content is greater than 3.3%,and the probability of tiller forming an ear is also above 60%.Therefore,at the jointing stage,the dry matter weight of stems and tillers and the nitrogen content of leaves can be measured by sampling in the field to preliminarily judge the status of tillers and panicles,and provide a reference for the rational regulation of the population.3.The regulatory mechanism of strong and weak granules that nitrogen fertilizer and density affect protein contentIn theory,the total protein content of wheat can be regarded as the weighted average result of the grains nitrogen content at different grain positions of each tiller.The protein content of grains at different grain positions in the main stem and each tiller showed the following order:strong grains>medium potential grains>weak grains,among which the strong grains had a strong positive regulation effect on the protein content of a single ear,and the main stem,1N,2N single grains had a strong positive regulation effect.The spike protein content has a main positive regulatory effect on the total protein content of the population.Therefore,including main stem,1N,2N strong grains and medium potential grains,the stem tiller and grain position with positive regulation effect are the key to the stable formation of proteins.Increasing nitrogen fertilizer application can reduce the difference of protein content between medium and strong grains.Density reduction and nitrogen increase were beneficial to promote the increase of grain protein content and reduce the differences between varieties and between stems and tillers.Tillers with low probability of panicle formation also have a certain negative effect on the quality of strong grains or medium-potential grains,but the weak grains of high-rank tillers are the grain positions with the greatest negative effect.Nitrogen application can increase the regulating effect of grain position which has a positive effect on quality.4.Regulatory effect of different grain positions and grain weights on grain protein contentAnalysis of the protein content of grains at different grain positions shows that,except for a few weak grains whose protein content is lower than 14%which is the strong gluten wheat standard.The protein content of strong grains,medium grains and most of the weak grains can exceed 14%and have positive regulatory effects on quality.When the single-grain weight of strong grains in 40 mg～50 mg,and single-grain weight of medium-potential grains in 35 mg～50mg,the protein content is basically higher than 15%,which has a great positive effect on improving wheat quality;when the single-grain weight of weak grains is less than 35 mg,its protein content conforms the national standards,whether higher than 35 mg,about with a one-third probability,its protein content has a large negative effect on quality.Therefore,we should make full use of cultivation measures to adjust the grain weight of strong gluten wheat to lay a foundation for high quality and stable yield.5.Physiological analysis of yield-quality synergy in strong gluten wheatThe experimental results analyzed the mechanism of wheat yield and quality formation from different physiological perspectives of wheat tillers,leaves and grains.The occurrence and growth of wheat stems and tillers are significantly regulated by endogenous hormones.The contents of IAA and ZR are the main hormones that affect the growth of stems and tillers.The level and stability of their ratios can regulate the tillering and panicle formation of wheat.The smaller the difference between the main stems and the variation less than 10%,the higher the probability of panicle formation.Too high density is not conducive to the stability of the photosynthetic performance of tiller flag leaves.Nitrogen fertilization can reduce the difference between tiller and main stem flag leaves.A reasonable combination of nitrogen density can stabilize the photosynthetic rate and photosynthetic pigment content of the flag leaves of the tiller and the main stem,and improve the uniformity and consistency of Pn among the flag leaves of each stem,which is the basis for stable yield.The effect of nitrogen fertilizer and density on the GS activity of high-rank tiller grains was greater than that of low-rank tiller.The application of nitrogen fertilizer can reduce the difference between the GS activity of tiller grains and the main stem,which is the key to improve and stabilize the protein content.6.Cultivation measures of yield and quality synergy and stability of strong gluten wheatUnder the condition of 2.7 million basic seedlings per hectare,applying 240 kg nitrogen,the main stem,1N and 2N should be fully used to form panicles,1N-1 and 3N compensation should be strived for supplemented by regulation and utilization can achieve a synergistic increase in yield and quality.