Breeding Selection On 52 Genes Controlling Yield,Quality,Stress Resistance And Adaptation In Commom Wheat

In order to meet the urgent food demand,intensive wheat breeding over the last 100 years has been implemented to improve traits including grain yield,quality,stress resistance and adaptation.This not only resulted in significant phenotypic variations,but also leaved footprints of artificial selection at the targeted genomic regions.With the great development of crop genomics,especially popularization of high-throughput genotyping technology,it becomes possible to discover favorable alleles of genes selected during breeding in wheat.In this study,a total of 1152 diverse global wheat collections were genotyped based on 52 KASP markers from cloned genes for agronomic traits including grain yield,quality,adaptation and stress resistance.Selection signals during improvement were explored to definite selective imprinting on genome.In addition,gene flow and allelic variations of functional genes in global wheats were compared to demonstrate the contribution of introduced accessions to Chinese wheat breeding.The results were shown as follows:1.Of 52 genes for agronomic traits used in this study,47 are polymorphic and 5 are monomorphic with only one allele.Phylogenetic analysis and principal component analysis(PCA)using 47 polymorphic genes showed that all materials were divided into two groups clearly referred to as Chinese wheat resources and introduced cultivars.Furthermore,the accessions from China were divided into two subgroups,Chinese landraces and modern Chinese cultivars.In addition,the introduced cultivars were subdivided into four subgroups,including Europe,CIMMYT,former USSR and North America,which exhibited a good geographic distribution pattern.2.A significant change was found in each trait when the Chinese wheat panel including 157 landraces and 323 modern cultivars was evaluated for 11 grain yield and adaptive traits in three environments.In comparison to landraces,heading date and flowering date were selected earlier and plant height was reduced in modern cultivars.Meanwhile,kernel numbers per spike,1000-kernel weight,kernel length,kernel width and kernel thickness were significantly increased,but effective tiller number,spike length,spikelet number per spike were decreased in modern cultivars.Correlation analysis of favored allele numbers with yield and adaptive traits showed that the accumulation of favorable alleles at yield genes significantly increased kernel width and 1000-kernel weight,but had a little effect on kernel numbers per spike and effective tiller number.The accumulation of favorable alleles at adaptive genes made heading earlier and plant height reduced.3.Based on 47 polymorphic genes,the mean gene diversity of modern Chinese cultivars was estimated as 0.32,which was significantly higher than that of Chinese landraces(0.26).Population genetic differentiation measured with Wright's Fst further revealed that genetic divergence was obvious during breeding periods.A total of 35 alleles of selected genes were identified through comparing frequency spectra using Z test.Of the 31 genes for grain yield,quality and stress resistance,17 positive prolonged genes that meant the favorable alleles increased significantly and 14 negative genes with the favorable allele frequencies decreased obviously from Chinese landraces to modern Chinese cultivars were found during different periods.Allele frequencies of Rht-B1 b,Rht-D1 b,vrn-D1 and Ppd-D1-2kb Del for four adaptive genes showed significant differences between Chinese landraces and modern Chinese cultivars.Favorable allele analysis showed the selection of improvement was the strongest in grain yield,following stress resistance,and the weakest in quality.4.Gene flow analysis showed that there were gene flows in different degree between accession from China and other countries,but it was most frequent comparing of the modern Chinese cultivars with the former USSR and Italy.Allele frequencies of 47 genes were evaluated in the global wheat according to their geographic distributions.Accessions from five different regions have their unique characteristics at 47 polymorphic genes.The spring type allele(Vrn-B1 b and Vrn-D1a)and photoperiod insensitive allele(Ppd-D1-2kb Del)predominated in both modern Chinese cultivars and CIMMYT cultivars.The accessions from China and former USSR had higher favorable allele frequencies in grain yield genes.For example,alleles controlling higher grain weight including Sus1-7A-Hap-H,Sus2-2B-Hap-H,and GW2-6A-Hap-A were present at high frequencies in cultivars from China and former USSR.The variability at various loci affecting quality indicated a greater influence of CIMMYT than other regions in breeding for quality traits.These alleles influenced hard grain texture(Pina-D1b),low PPO activity(Ppo-A1 b and Ppo-D1a)and lower yellow pigment content(Zds-A1a).For stress resistance,the average favorable allele frequency predominated in Europe compared with other regions,such as two genes governing drought tolerance(Dreb-B1 a and 1-fehw3-Westonia type),one for low pre-harvest sprouting(MFT-A1-PHS+)and one for leaf rust resistance(Lr68+).Therefore,the introduction and utilization of excellent foreign germplasm resources is still an important way to widen the genetic basis of wheat in China.