Molecular Mapping Of Two Powdery Mildew Resistance Genes And One Leaf Rust Resistance Gene In Wheat Relatives

Powdery mildew and leaf rust,caused by Blumeria graminis f.sp.tritici(Bgt)and Puccinia recondite f.sp.tritici respectively,are two important fungal diseases of wheat worldwide.Deployment of resistant cultivars is one of the safe,environmental friendly and effective approaches to control the diseases.Exploiting diversified germplasms and discovery of new resistance genes is considered to be the basic work for resistance breeding.Wheat relatives are the major genetic resources to be utilized for wheat breeding.Spelt wheat(Triticum aestivum ssp.spelta 2n=6X=42,AABBDD)and wild emmer wheat(T.dicoccoides,2n = 4x = 28,AABB)are close relatives of common wheat(T.aestivum)and contain abundant genetic diversity of resistance genes for wheat improvement.We report the identification and mapping of a powdery mildew resistance gene in spelt wheat cultivar Hubel,which was introduced to China from Europe and was resistant to Chinese Bgt isolate E09 at the seedling stage.The parent Liaochun10 and F1 of Hubel X Liaochun10 are both susceptible,which suggested the resistance gene(s)in Hubel is recessive.Genetic analysis of a recombinant inbred line(RIL)population derived from a cross of Hubel and a susceptible early maturing mutant line indicated that Hubel possessed a single powdery mildew resistance gene(temporarily designated as MlHubel).Markers linked to MIHubel were identified using bulked segregant analysis(BSA)to screen wheat simple sequence repeat(SSR)and expressed sequence tag(EST)-derived sequence tagged site(STS).The linked markers were physically located on wheat chromosome 2D by the nullisome-tetrasome analysis with Chinese Spring homeologous group 2 nulli-tetrasomic lines.Comparative genomic analysis indicated that the genetic interval covering MIHubel in wheat is highly co-linear with the corresponding regions on Brachypodium distachyon chromosome 5 and Oryza sativa chromosome 4.Accordingly,the genetic map of MIHubel was established with comparison to B.distachyon 5L and O.sativa 4L and discovered and identified 14 EST-STS markers are tightly-linked to MIHubel,then we constructed genetic map with all the SSR and EST-STS markers.With the closest marker Xgwm265 being 0.4 cM from MIHubel.The identification of the recessive powdery mildew gene in spelt wheat suggests the potential of this accession along with its closely linked markers in breeding for resistance to powdery mildew.We identified introgression line 1A509 resistant to powdery mildew.This resistant line was made by crossing the resistant wild emmer accession Iw30 with susceptible common wheat cultivar Zheng98 and backcrossing 3 times with common wheat 87-1(the pedigree of 1A509 was IW30/Zheng98//87-1/3).Then a population of F2 derived F3 families was obtained from a cross between 1A509 and the susceptible cultivar Liaochun 10.Genetic analysis of this population for the powdery mildew resistance with the Bgt isolate E09 indicated that the powdery mildew resistance is controlled by a single dominant gene,temporally designated as MLIW30.Four SSR markers and one STS marker linked with MLIW30 were acquired by BSA of wheat molecular markers.Finally,this gene was located on the long arm of chromosome 4A and flanked by two wheat SSR markers Xgm160 and Xgwm350 in a 5.0 cM interval.Since no powdery mildew resistance gene from wild emmer wheat has been found on the long arm of wheat chromosome 4A,MLIW30 might be a novel resistance locus.It was previously reported that a leaf rust resistance gene known as LrAlt was in spelt wheat accession Altgold and located on the distal part of the short arm of wheat chromosome 2A.Using comparative genomics analysis,we found that the resistance gene region on 2AS was orthologous to Brachypodium chromosome 5 and rice chromosome 4.Based on wheat-Brachypodium-rice genomic colinearity,EST-STS markers linked to LrAlt,including BE498683,BE471132.1,BG605273,CD454629,and others,were designed and verified.Seven EST-STS markers and 2 SSR markers were identified and the genetic map of LrAlt was constructed.This study has enriched the resistance genes for wheat breeding.The molecular markers identified in this study provide basic information for fine mapping,molecular assisted selection,and gene pyramiding of the target genes.