| Understanding the difference of main agronomic traits in wheat between low-density and high-density planting can provide evidences for wheat breeding of high yield and stability selection.One hundred and ninety-seven wheat lines from Huanghuai Southern winter wheat region were planted at Zhengzhou Scientific Research and Education Center of Henan Agricultural University in 2014-2015 and 2015-2016 cropping seasons,and fourteen main agronomic traits were investigated to analyze the differences between low-density and high-density planting conditions.The GWAS analysis was performed using the 35 K chip test results.The main results are as follows:1.Extremely significant difference existed in twelve traits between low-density and high-density planting conditions,while no significant difference was found in flag leaf angle.Compared with the low-density planting condition,the heading date and flowering date of materials in the high-density condition were 1.22 days and 1.02 days earlier,respectively.Meanwhile,plant height,neck length and internode length under spike increased by 4.37 cm,1.84 cm and 1.01 cm,respectively.In contrast,the flag leaf length,flag leaf width and spike length averagely reduced by 0.36 cm,0.10 cm,0.17 cm,respectively.The fertile spikelet number reduces by 1.71,whereas the infertile spikelet number increased by 1.01.In addition,grains per spike,thousand grain weights,single spike weight averagely reduced by 9.85,1.53 g,0.62 g,respectively.However,the range of variation in different traits was relatively large,indicating the large difference between varieties,which was also a reflection of wheat yield stability.The comprehensive evaluation of different varieties found that varieties less sensitive to planting models were mostly historical varieties with higher plant height,only a few varieties such as Pumai 053,Zhongyu 9302 and Hongmai 118 were the current popular varieties.2.All of the fourteen traits are significantly positively correlated with each other under the low and high-density planting modes.While,the degrees of correlation varied greatly with different traits.Among them,the correlation coefficient of heading stage,flowering stage and plant height reached above 0.97,which indicated that the performance of varieties under low density planting were consistent with the materials under the higher density environment.We can predict the character performances of high-density condition more accurately by low-density planting model with the help of regression equation.The correlation coefficient of the grain number per spike is less than 0.7,which showed poor consistency between low-density and high-density planting conditions.Other traits were at the middle levels.Stepwise regression analysis was performed on the planting high-density yield(y)as dependent variables and the low-density traits as independent variables,and very significant regression was found for plant height(x2),neck length(x3),thousand grain weight(x4)and single spike weight(x5)of dense planting,while significant for heading date(x1).The optimal regression equation was y=626.71+3.42x1-3.44x2-7.36x3+3.13x4+48.55x5?3.Four hundred and forty-seven loci associated with agronomic traits were found by association analysis,which distributed in the 21 chromosomes of wheat,and the phenotypic variation contribution rate(R2)ranged from 5.69% to 12.16% for individual loci.Thirty-two of the loci were repeatedly associated in two environments.Further analysis of the association sites explored a number of dominant alleles related to difference of agronomic traits,such as AX-95123073 in 2B and AX-94603856 in 2D,which were significantly associated with differences in heading date and flowering date.Twelve SNPs with a significant difference in the number of infertile spikelets were distributed in 4A,4B and 4D.Finally,we found thirty-six materials with higher proportion of density-insensitive sites,such as Luomai 18,and these markers can be used in selection of individual plants. |
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