Fine mapping of powdery mildew resistance gene PmTm4 in wheat using comparative genomics

Powdery mildew,caused by Blumeria graminis f.sp.tritici,is one of the most severe wheat diseases.Mining powdery mildew resistance genes in wheat cultivars and their appliance in breeding program is a promising way to control this disease.Genetic analysis revealed that a single dominant resistance gene named PmTm4 originated from Chinese wheat line Tangmai 4 confers resistance to prevailing isolates of B.graminis f.sp.tritici isolate E09.Detailed comparative genomics analyses helped to develop closely linked markers to PmTm4 and a fine genetic map was constructed using large F2population,in which PmTm4 was located into a 0.66-c M genetic interval.The orthologous subgenome region of PmTm4in Aegilops tauschii was identified,and two resistance gene analogs（RGA）were characterized from the corresponding sequence scaffolds of Ae.tauschii draft assembly.The closely linked markers and identified Ae.tauschii orthologs in the mapping interval provide an entry point for chromosome landing and map-based cloning of PmTm4.

Comparative genetic mapping revealed powdery mildew resistance gene MlWE4 derived from wild emmer is located in same genomic region of Pm36 and Ml3D232 on chromosome 5BL

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most devastating wheat diseases. Wild emmer wheat（Triticum turgidum ssp. dicoccoides） is a promising source of disease resistance for wheat. A powdery mildew resistance gene conferring resistance to B. graminis f. sp. tritici isolate E09, originating from wild emmer wheat, has been transferred into the hexaploid wheat line WE4 through crossing and backcrossing. Genetic analyses indicated that the powdery mildew resistance was controlled by a single dominant gene, temporarily designated Ml WE4. By mean of comparative genomics and bulked segregant analysis, a genetic linkage map of Ml WE4 was constructed, and Ml WE4 was mapped on the distal region of chromosome arm 5BL. Comparative genetic linkage maps showed that genes Ml WE4, Pm36 and Ml3D232 were co-segregated with markers XBD37670 and XBD37680, indicating they are likely the same gene or alleles in the same locus. The co-segregated markers provide a starting point for chromosome landing and map-based cloning of Ml WE4, Pm36 and Ml3D232.

Characterization of RAPD Markers,and the RFLP Marker Linked to Powdery Mildew Resistance Gene Derived from Different Accessions of H.villosa

The analysis was carried out on performance of the resistance gene from Haynaldia villosa accession of the former Soviet Union to different isolates of Bluemerie graminis. Polymorphisms were revealed between 6D/6V substitution line Pm930640 and its pedigree parents using five RAPD markers of OPAN031700, OPAI01700, OPAL03750, OPAD07480 and OPAG15580 screened out from 120 random 10-mers primers. Three RAPD markers of OPAN03, OPAI01 and OPAL03 were linked with the resistance gene by analysis of F2 population of Chancellor×Pm930640. Analysis of 29 wheat lines including part of lines conferring the known genes from Pm1 to Pm20 respectively, lines conferring resistance gene from two H. villosa accessions and the related wheat parents, were analyzed and the results showed that these markers not only linked to the gene resistant to powdery mildew from H. villosa, but also detected different genetic backgrounds. OPAL03750 can be used as the marker to distinguish the different resistant lines from two H. villosa accessions because it was only observed in the materials from H. villosa of the former Soviet Union. RFLP analysis also showed the polymorphisms between two H. villosa accessions and their derived resistant lines.