Nitrogen Efficiency Evaluation Screening Of Wheat Germplasm Resources And Genome-wide Ssociation Analysis Of Related Traits

Since the recent agricultural revolution,large amounts of nitrogenous fertilizers have been applied to increase wheat yields,resulting in problems such as low fertilizer use efficiency and environmental pollution.Evaluation and screening of wheat N-efficient utilization germplasm resources,identification of N-efficient utilization genetic loci and breeding of N-efficient utilization varieties are environmentally friendly ways to improve fertilizer utilization.In this study,a natural population of 325 wheat varieties(lines)from different countries,including China and abroad,was grown under no and normal nitrogen application conditions for two consecutive years from 2019 to 2021 to examine agronomic and quality traits such as plant height,flag leaf length and width,and thousand grain weight,and to assess the low nitrogen tolerance of wheat varieties(lines).Genome-wide association analysis was performed using 90 k microarrays to explore SNP loci associated with the above phenotypic traits.The main findings are as follows.(1)The agronomic and quality traits of the participating materials were significantly different and normally distributed.The mean values of protein content,wet gluten content and other grain quality traits were significantly stressed by nitrogen,and their mean values were about 25% lower under low nitrogen conditions than under high nitrogen conditions.Yield traits such as 1000 grain weight,number of spikelets and number of fertile spikelets varied significantly under low N stress,with their mean values being about 5% lower under low N conditions than under high N conditions.Agronomic traits such as plant height and flag leaf length and width varied next,mostly around 4%,while seed length and width traits were the weakest,varying around 1.5%.(2)The results of the correlation analysis of the PI values of the low nitrogen tolerance coefficients of the traits in the test materials indicated that: 1,000 grain weight was highly significantly and positively correlated with seed length,seed width,number of fertile spikelets and number of grains,with the largest correlation of 0.34 with grain width,but significantly and negatively correlated with plant height;spike length was highly significantly correlated with flag leaf length,number of fertile spikelets,number of grains,stem thickness,grain length and grain width,and significantly correlated with 1,000 grain weight.Protein content,wet gluten content,starch content and sinker value were all highly significantly correlated with each other.(3)Based on the D values of 325 wheat varieties(lines)for low nitrogen tolerance,wheat was divided into four categories,with category 4 being the low nitrogen sensitive type,accounting for 10.47% of the total varieties,including 34 varieties such as Jining 3,Tanong 7018 and Shi 4185;category 3 being the low nitrogen more sensitive type,including 102 varieties such as Huangxian Large Grain Semi-Awn,Lumai 1,Qida 195,Yanong 19 and Lankao 198.The second category is the intermediate type,which includes Bi-An 1,Shan Nong 12,Xin Mai 11,Yun Dao 2130 and Nong Da 211,accounting for 32%of the total;the first category is the low-nitrogen tolerant type,which includes Bai Gao 38,Bi-An 4 and Xi Nong 529,accounting for 22.15% of the total.Fourteen varieties were screened for nitrogen tolerance and high thousand grain weight,and 14 varieties were selected for breeding.(4)Based on the gene chip data of 325 wheat varieties,they were divided into four subgroups,subgroup 1(Sub1),subgroup 2(Sub2),subgroup 3(Sub3)and subgroup 4(Sub4)containing 90,46,55 and 121 wheat materials respectively.Linkage disequilibrium LD analysis was performed using SNP markers distributed on 21 chromosomes,where the LD attenuation distance was determined by reducing the LD coefficient to half of the maximum value,which was about 1.5 Mb.Genome-wide association analysis of agronomic and seed traits showed that a total of 35 QTLs were delineated,with phenotypic variance contribution(R2)ranging from 4.80% to 10.51%.Twenty-three QTLs loci were detected in two environments,ten QTLs loci were detected in three environments and two QTLs loci were detected in four environments.Among them,the maximum number of MTASs significantly associated with plant height(PH)was 17 in total,with contribution rates(R2)ranging from 4.80% to 10.51%.(5)Based on the QTLs delineated by significant loci,BLAST was performed on the IWGSC website to screen for important candidate genes associated with low nitrogen tolerance traits for thousand grain weight.The candidate gene functions included genes regulating cellulose synthase and serine/threonine protein kinase,and ubiquitin biosynthesis COQ9-like proteins.The results of the study provide an evaluation method for evaluating the nitrogen efficiency of wheat,and the germplasm resources for efficient nitrogen utilization can be mined and screened,and the corresponding molecular markers can be developed for marker-assisted nitrogen efficiency variety selection.