Effect Of Shading And Plant Density On Lodging Resistance Of Culm In Winter Wheat

Wheat is one of the three major food crops in China.In the practice of high yield and high yield cultivation of wheat,increasing planting density is one of the important measures to improve the yield of wheat.However,the growing population has seriously exacerbated the contradiction between wheat groups and individuals.The deterioration of population structure and the deterioration of individual stem development quality lead to lodging,resulting in yield reduction.At the same time,with the rapid development of industry and the aggravation of environmental pollution,the solar radiation reaching the earth’s surface is significantly reduced,and the lack of light resources has become another important limiting factor for crop production in China.Therefore,the effects of shading and density on lodging resistance of winter wheat stem were studied to provide theoretical basis for the rational population construction of winter wheat under the background of global climate change and the breeding and screening of lodging-resistant and shade-tolerant varieties.In the experiment,two winter wheat varieties Shannong 16（lodging sensitive type）and Shannong 23（lodging resistant type）with different lodging resistance were selected as experimental materials.Three shading periods were set:no shading（S0）,jointing stage shading（S1）,jointing stage to maturity stage shading（S2）,with shading degree of 50%.Three planting densities were set:1.5 million plants/ha（D1）,2.25 million plants/ha（D2）,and 3 million plants/ha（D3）.The photosynthetic efficiency of wheat leaves under shading at jointing stage was analyzed and compared,as well as the effects of shading on dry matter accumulation and stem dry matter output ratio of aboveground organs at flowering and maturity stages of different populations of wheat,plant height,internode length,center of gravity height,stem diameter,wall thickness,filling degree of stem,breaking strength,lignin content,lignin monomer group and yield of plant apparent traits.At the same time,the effect of shading on the expression of key enzyme genes in lignin synthesis pathway was further determined.The main research results are as follows:（1）Shading at jointing stage had significant effects on photosynthetic performance and dry matter accumulation of functional leaves of winter wheat.Under shading treatment,the light interception of winter wheat population decreased,the chlorophyll content of winter wheat functional leaves increased,the net photosynthetic rate（Pn）significantly decreased,On the 0th day after removing jointing stage,Pn of SN16 and SN23 shading treatments decreased by 20.84%and 24.51%compared with S0,respectively.the intercellular CO₂ concentration（Ci）increased,and the stomatal conductance（Gs）decreased.The decrease of photosynthetic capacity led to the decrease of dry matter accumulation in winter wheat,and significantly reduced the storage of stem-sheath assimilates.The translocation rate of stem-sheath assimilates to grains and the output rate of stem-sheath assimilates increased in the late flowering stage,which significantly reduced the stem plumpness between the second internode of the base（2）The plant height and basal internode length of winter wheat increased significantly with the increase of planting density and shading at jointing stage,while the diameter and wall thickness of the second basal internode decreased significantly,and the folding resistance decreased significantly.Under different shading treatments,the overall trend of the resistance of the two varieties was S0>S1>S2.Under different densities,except for the lodging-sensitive varieties SN16 at milk-ripening stage under S1 and S2 treatments,the order was D2>D1>D3.Under other treatments,the folding resistance decreased with the increase of planting density at different stages,which was D1>D2>D3.（3）Shading and density treatments significantly affected lignin synthesis in basal internodes of winter wheat.With the increase of planting density and shading time,lignin accumulation gradually decreased.At the same time,the content and proportion of lignin monomers S（syringyl lignin）and G（guaiacyl lignin）gradually decreased,and H-type monomer（p-hydroxyphenyl lignin）increased.Shading treatment significantly reduced the expression of key enzyme genes of lignin biosynthesis pathway in wheat basal internode 2,such as Ta PAL（phenylalanine ammonialyase）,Ta CCR（cinnamic acyl coenzyme A reductase）,Ta CAD（cinnamic alcohol dehydrogenase）and Ta COMT（caffeic acid3-methoxymethyltransferase）.（4）The response of yield components of winter wheat to planting density was as follows.With the increase of planting density,the number of spikes per unit area of winter wheat increased,and the spike grains and 1000-grain weight decreased.The response to shading showed that with the extension of shading time,the number of spikes,grains per spike and 1000-grain weight per unit area of winter wheat decreased significantly.Under the same shading treatment,the yield reduction rate of D3 was the highest,and under the same density treatment,yield reduction was as high as 58.05%,shading from jointing stage to maturity stage had the greatest impact on yield.