| Powdery mildew,caused by the biotrophic fungus Blumeria graminis f.sp.tritici（Bgt）,is a widely occurring wheat disease and poses a serious threat to wheat production and quality.Utilization of the cultivars with sufficient levels of powdery mildew resistance is the most practical and cost-effective mean to control this disease.However,the rapid evolution of new Bgt races often leads to loss of effectiveness,and necessitates searches for new sources of resistance.The wild relatives of wheat provide an important source of genetic variation for wheat improvement.Most species belonging to the tertiary gene pool of wheat are not common hosts of Bgt and their resistance is usually broad-spectrum and apparently effective over long evolutionary periods.Among these Dasypyrum villosum（2n=14,VV）is recognized as an excellent gene pool for taping into new Pm resistance genes because of its immunity response to all Bgt isolates of wheat.Four formally designated powdery mildew resistance genes,Pm21,Pm55,Pm62 and Pm67,have been transferred from D.villosum into wheat by means of compensating Robertsonian translocations（RobTs）,which reveals that D.villosum is an important source for new powdery mildew resistance gene of wheat.In the present study,we described and genetically mapped chromosome arm 5VS#5 to confer effective resistance against Bgt,and introgress this powdery mildew resistance gene Pm5V into wheat through the breakage-fusion mechanism for providing new resistance germplasm in breeding.The results as followings:1.Development of new wheat-D.villosum 5V#5 introgression lines and characterization of powdery mildew resistance gene Pm5V in wheatIn the progeny of（ZY1286×01I140）/NAU0686//4*NAU0686 BC4F2,four wheat-chromosome 5V#5 introgression lines were developed,including a homozygous T5DL·5VS translocation line TF5V-11,a homozygou small-segment T7DL.7DS-5VS translocation line NAU18511-12（FL 0.50-1.00）,a chromosome 5V disomic addition line NAU1857-2 and a 5VS#5 ditelomic addition line NAU1857-10.Powdery mildew evaluation showed that the four lines were all immune response to powdery mildew at the seedling and adult plant stages when inoculated with mixture races of Bgt.Genetic analysis indicated that the T5DL.5VS#5 translocated chromosome transmitted normally in wheat background,and the powdery mildew resistance was co-segregation with the alien chromosome,which further confirmed that a seedling resistance gene was located on the D.villosum 5VS#5 FL0.50-1.00 segment,temporary named Pm5V.The independent identification of Bgt isolates at seedling stage revealed that the line with Pm5V gene showed highly resistance levels to 24 isolates of Bgt,which is different from the response spectrum of the line with Pm55 gene.2.Genetic analysis and mapping of Pm5VIn order to clarify the pairing behavior between the chromosome arms of 5VS#4 and 5VS#5,two wheat-D.villosum T5DL.5VS translocation lines TF5V-2 and TF5V-11 were crossed to obtain the F1 hybrids and F2 and F2:3 segregating populations.The pollen mother cells（PMCs）of their F1 hybrids were observed by genomic in situ hybridization（GISH）.Result showed that the two translocated chromosomes paired and separated normally.In addition,polymorphic markers between 5VS#4 and 5VS#5 were screened from EST,SSR,and IT markers developed based on wheat 5DS sequences.As well as the Wheat 660K single nucleotide polymorphism（SNP）array and contigs harbouring NLR sequences information of D.villosum were used to develop polymorphic markers.Finally,27 pairs of polymorphic molecular markers between the two 5VS chromosome arms were used to genotype F2 individuals.The separation of the resistance and susceptible plants of the 222 F2 individuals derived from the crossing TF5V-2 × TF5V-11 was fit to 3:1 ratio at the seedling stage,indicating that a single dominant resistance gene in TF5V-11.Meanwhile,nine plants were susceptible at the adult plant stage,suggesting that Pm5V and Pm55 are nonallelic genes.In addition,the genetic mapping and chromosome physical location analysis by using Pm2 specific markers showed that Pm5V is not a Pm2 homologous.Finally,a 5VS chromosome arm genetic linkage map with 27 markers was conducted by using JoinMap 4.0 software,and Pm5V gene was initially located between the markers CINAU5VS-10 and CINAU5VS-18 with a genetic distance of 0.2 cM and 0.1 cM,respectively.Based on the collinear between the chromosome arms of 5VS and 5DS,the linkage markers were physically mapped to the specific Chinese spring 5DS chromosome bin. |
