Identification Of QTLs In Wheat Grain Protein And Its Selection And Utilization In Modern Breeding

Wheat(Triticum aestivum L.)is one of the crops with the largest planting area,the highest output and nutrition,and the largest number of processed products in the world.Wheat quality traits are the quantitative traits controlled by multiple genes and with complex genetic basis.It is of great practical significance to use high density SNP markers for identifying potential genetic loci and improving the understanding of the genetic pleiotropy of wheat quality traits.In recent years,the sowing date of wheat is delayed and the growth period suffers from high temperature because of the frequent rainy during wheat sowing,which affects the grain filling and quality formation.The identification of genetic loci that can maintain stable yield and quality under different sowing dates can provide a solution to coordinate the relationship between high yield and high quality under the future climate change,which is of great significance to ensure national food security and meet consumers’ demand for the quality of wheat products.Five major quality traits were performed a phenotypic investigation and resampling GWAS analysis with a 406 wheat natural accessions under eight environments in this study.The objective was to: identify the key genetic loci regulating the main quality traits of wheat,and analyze their selection and application in the main wheat areas,providing an reference for their application in future molecular breeding.By comparing the effects of different sowing dates on the main quality traits of wheat,the genetic loci that can maintain yield and improve quality under late sowing conditions were excavated,which provided a new idea for late sowing-resistant wheat breeding.The main results are as follows:1.Phenotypic analysis of five main quality traits showed that the grain protein content,wet gluten content,sedimentation value,moisture absorption and water content displaying the continuous variation and normal distribution in the natural population.Grain protein content,wet gluten content,sedimentation value and water content showed a significantly positive correlation with each other.By contrast,water content showed a significant negative correlations with moisture absorption.2.A total of 130 significant SNPs were identified by GWAS of five main quality traits,which could be divided into 41 QTLs.15,13,5,4 and 4 QTLs were identified in grain protein content,wet gluten content,sedimentation value,moisture absorption and water content,respectively.Among them,7 QTLs showed pleiotropy and their superior haplotype could significantly increase grain protein content,wet gluten content and sedimentation value simultaneously.3.The results of GWAS of grain protein content were analyzed,and four QTLs have been repeatedly reported in previous studies.Haplotype analysis showed that their haplotype B could significantly increase grain protein content.But these four QTLs have not been selected in modern cultivars.Further analysis of the distribution of different haplotypes of the four QTLs in different wheat regions showed that the frequency of haplotype B decreased significantly in Yellow and Huai wheat zone,and the corresponding grain protein content also decreased significantly.Haplotype interaction analysis showed that QGPC-4B.1b and QGPC-6D.2b,QGPC-5B.1b and QGPC-7B.1b had an additive effect,which could be combined to improve the protein content of wheat.4.The correlation analysis between the yield-related traits and grain protein content showed that kernel number per spike and thousand kernel weight had a significantly negative correlation with grain protein content,while productive tiller number had a significantly positive correlation with grain protein content.By analyzing the effects of four reported QTLs related to protein content on yield-related traits,it was showed that QGPC-4B.1b could significantly increase thousand kernel weight and decrease kernel number per spike,which was also supported by the result of GWAS.QGPC-4B.1b played a regulatory role in coordinating the relationship between stable yield and high quality of wheat.5.Compared with normal sowing condition,the grain protein content,wet gluten content and sedimentation value were significantly increased under late sowing condition,while moisture absorption and water content were significantly decreased.A total of 182 SNPs significantly associated with the stress sensitivity index were identified by GWAS,which could be divided into 59 QTLs.12,7,18,9 and 13 QTLs were detected in GPC-SSI,WGC-SSI,SV-SSI,MA-SSI and WC-SSI,respectively.By analyzing the results of twice GWAS,it was found that five QTLs could be associated with both stress sensitivity index and quality phenotype,among which the superior haplotype of QP-5A.1 could improve wheat quality and heat tolerance without yield reduction.These results enrich the genetic analysis basis of the main quality traits of wheat,and identify the loci that can simultaneously regulate the yield,quality and stress resistance of wheat.These results provide an important reference for the application of molecular design and breeding in the future,and provide a theoretical basis for breeding new wheat varieties with high yield and quality.