Genetic Mapping Of Powdery Mildew Resistance Genes In The Eight Common Wheat Acessions

As the second largest grain crops in China,its production and quality are related to national food security.Powdery mildew caused by Blumeria graminis f.sp.tritici（Bgt）is one of the three major diseases of wheat,which can lead to wheat production failure in severe cases.At present,the most economical and effective measures to control powdery mildew is to excavate the powdery mildew resistance genes in wheat and promote the planting of resistant disease varieties.In this study,729 common wheat acessions were identified for resistance,and 8 excellent powdery mildew resistant germplasm were selected.The resistance genes were identified through resistance genetic analysis,bulk segregatant analysis（BSA）and molecular marker mapping.The specific research results were as follows:In the previous study,729 common wheat acessions were identified by inoculating Bgt isolatesE09 and E23-1.In this study,the eight excellent powdery mildew resistant materials such as Tukaminia,Alson,Safha3,Longbow,Knirps,Xinxiang9178,Flanders and Honghuamai were seleced crossing with powdery mildew susceptible materials including Zhoumai18,Yangmai158,Kenong199 and Ningmaizi119.Resistance inheritance showed that,5 germplasm containing Tukaminia,Alson,Safha3,Longbow and Knirps carry a dominant powdery mildew resistance gene,temporarily named Pm TMN,Pm ASN,Pm SFA,Pm LGW and Pm KIS respectively;Xinxiang9178 and Flanders carry a recessive powdery mildew resistance gene,temporarily named Pm XX9178 and Pm FNS respectively.Combination of BSA and known linkage markers of published powdery mildew resistance genes showed that,Pm ASN and Pm LGW are likely to be allelic or closely linked to known Pm2;Pm TMN is located in the 30-50 Mb region of 1DS chromosome,diagnostic marker MP1362 indicates that the gene was different from the known gene Pm24;Pm XX9178 is located in the 90-120 Mb region of 2BS chromosome and its relationship with the known genes Pm42 is unknown;Pm KIS is located in the 50-75 Mb region of 5BS chromosome and cannot be distinguished from the known gene Pm30 temporarily;Pm SFA is located in the 150-200 Mb segment of 1AS chromosome,which is different from the known gene Pm3 in this segment according to the amplification results of molecular markers;Pm FNS is located at 30-60 Mb of 2BS chromosome,which is different from the know genes sach as Pm26、Pm42、Pm49、Pm62 and Pm68 in this chromosome,the physical positions of these genes are different from Pm FNS.No polymorphism marker had been found after analyzing the results of amplified molecular marker.It was speculated that safha3 and Flanders are likely to carry new powdery mildew resistance genes.Using Honghuamai and Ningmaizi119 as parents,orthogonal and antiintersection crosses were configured.E09 isolate was used to inoculate F₁ hybrids,F₂ populations and F_2:3 families.All reciprocal F₁are resistant to disease.Among the 5,264 F₂ plants of Ningmaizi119/Honghuamai,3,812 and 1,352 were resistant and susceptible,which was in line with the separation ration of 3:1（χ²=0.034,P=0.050）.Of which,the proportion of homozygous resistant families,heterozygous resistant families and homozygous susceptible families in some F_2:3 progenies was 36:78:40,which was in line with the separation ration of1:2:1（χ²=0.23,P=0.89）.Among 156 F₂ plants of Honghuamai/Ningmaizi119,the segregation ratio was115:41 fitting a 3:1 ratio（χ²=0.077,P=0.78）,and the number of homozygous resistant families,heterozygous resistant families and homozygous susceptible families was 36:79:41 respectively,which was also in line with the separation ration of 1:2:1（χ²=0.35,P=0.84）.Therefore,all genetic analyses of resistance indicated that Honghuamai carries a partially dominant powdery mildew resistance gene,temporarily named Pm HHM.The resistance and susceptibility pools of Pm HHM were scanned with a 55 K SNP chip of common wheat,and the polymorphic SNP were subsequently found in 700-750 Mb of 4AL chromosome.Therefore,SSR markers in this region were used to detect the genotypes of Ningmaizi119 and Honghuamai F_2:3 families,and the gene was initially located between Xgwm160 and Xwmc313 with the genetic distance of 11.1 c M.SSR markers were futher developed based on the Chinese Spring 4AL genome sequence,the target interval was narrowed to a genetic distance of 7.0 c M between Xmp1512 and Xwmc313,corresponding to the 6.96Mb on Chinese Spring reference genome.In order to map Pm HHM gene,1,352 F₂susceptible plants of Ningmaizi119/Honghuamai were amplified using bilateral markers MP1512 and WMC313,a total of 111 recombinant plants were detected,the recombinant was amplified using the developed polymorphic molecular markers MP1567,MP1439,MP1440,MP1442 and MP1444.The target gene location to Xmp1567（733.6 Mb）.-Pm HHM/Xmp1442/Xmp1440/Xmp1439-Xmp1444（738.1 Mb）,corresponding to the 4.46 Mb on Chinese Spring reference genome,the genetic range was 0.29 c M.The positions of all developed markers were well collinear with the Chinese Spring reference genome,however,there was significant inhibition of recombination in the Pm HHM region between the two parents.A total 264 genes were annotated in this region of the Chinese Spring reference genome,a large number of genes were deleted in Chinese Spring comparing the reference genome sequences of T.urartu,T.dicocoides and T.durum.Among 264 genes,there were 106 resistance gene-analogues（RGAs）distributing in clusters.Collinear analysis showed that 15RGAs had homologous genes in the three wheat related species.Comparing the published genes Pm61 and MLIW30 on chromosome 4AL,the positions of the two genes were obviously different from Pm HHM and Pm HHM is most likely a new powdery mildew resistance gene.The closely linked or co-separation markers developed in this study can be effectively used for marker assisted selection（MAS）of the gene.