Fine mapping of Pm58 from Aegilops tauschii conferring powdery mildew resistance.

KEY MESSAGE: The powdery mildew resistance gene Pm58 was traced to a 141.3-kb interval with the co-segregating marker Xkasp68500 in wheat breeding. Pm58 is a powdery mildew resistance gene identified in Aegilops tauschii accession TA1662 and effective in a common wheat background. To finely map Pm58, an F2 population of 676 plants derived from the cross T093 × TA1662 was used for recombinant screening. We obtained 13 recombinants that occurred between the flanking markers Xhnu670 and Xhnu186. Genotyping and phenotyping these recombinant F2:3 families delimited Pm58 to a 0.22-cM interval (Xsts20220-Xkasp61553) on chromosome arm 2DS. The region carrying the Pm58 locus was approximately 141.3-kb, which contained eight annotated genes according to the reference genome sequence of Ae. tauschii AL8/78. Haplotype analysis of 178 Ae. tauschii accessions using the candidate gene-specific markers identified a disease resistance gene AET2Gv20068500 as a candidate for Pm58. Comparative mapping of the Pm58-containing interval revealed two presence/absence variations (PAVs) between AL8/78 and common wheat Chinese Spring. PAV-1 resides in the 3'-end of AET2Gv20068500. The majority of 158 common wheat cultivars (84.8%) displayed the absence of a 14.1-kb fragment in the PAV-1 region, which was confirmed by aligning the targeted genome sequences of the other sequenced Ae. tauschii accessions and common wheat cultivars. A co-segregating marker Xkasp68500 developed from AET2Gv20068500 can distinguish TA1662 from all randomly selected common wheat cultivars and will be instrumental for tracking Pm58 in breeding programs.

Characterization of PmHHXM, a New Broad-Spectrum Powdery Mildew Resistance Gene in Chinese Wheat Landrace Honghuaxiaomai.

Powdery mildew, caused by fungal pathogen Blumeria graminis f. sp. tritici, is an agronomically important and widespread wheat disease causing severe yield losses. Deployment of broad-spectrum disease resistance genes is the preferred strategy to prevent this pathogen. Chinese wheat landrace Honghuaxiaomai (HHXM) was resistant to all 23 tested B. graminis f. sp. tritici isolates at the seedling stage. The F1, F2, and F2:3 progenies derived from the cross HHXM × Yangmai 158 were used in this study, and genetic analysis revealed that a single dominant gene, designated PmHHXM, conferred resistance to B. graminis f. sp. tritici isolate E09. Bulked segregant analysis and molecular mapping initially located PmHHXM to the distal region of chromosome 4AL. To fine map PmHHXM, we identified two critical recombinants from 592 F2 plants and delimited PmHHXM to a 0.18-cM Xkasp475200 to Xhnu552 interval covering 1.77 Mb, in which a number of disease resistance-related gene clusters were annotated. Comparative mapping of this interval revealed a perturbed synteny among Triticeae species. This study reports the new powdery mildew resistance gene PmHHXM, which seems different from three known quantitative trait loci/genes identified on chromosome 4AL and has significant values for further genetic improvement. Analysis of the polymorphisms of 13 cosegregating markers between HHXM and 170 modern wheat cultivars indicates that Xhnu227 and Xsts478700 developed here are ideal for marker-assisted introgression of this locus in wheat breeding.

Fine Mapping a Broad-Spectrum Powdery Mildew Resistance Gene in Chinese Landrace Datoumai, PmDTM, and Its Relationship with Pm24.

Powdery mildew, caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is a globally important wheat disease causing severe yield losses, and deployment of resistant varieties is the preferred choice for managing this disease. Chinese wheat landrace Datoumai was resistant to 22 of 23 Bgt isolates at the seedling stage. Genetic analysis based on the inoculation of Bgt isolate E09 on the F1, F2, and F2:3 populations derived from the cross Datoumai × Huixianhong revealed that the powdery mildew resistance of Datoumai is controlled by a single dominant gene, temporarily designated as PmDTM. Bulked segregant analysis and simple sequence repeat mapping with 200 F2 plants showed that PmDTM was located in the same genetic region as Pm24 on chromosome 1DS. To fine map PmDTM, 12 critical recombinants were identified from 1,192 F2 plants and delimited PmDTM to a 0.5-cM Xhnu58800 to Xhnu59000 interval covering 180.5 Kb (38,728,125 to 38,908,656 bp) on chromosome 1DS, and only one highly confident gene, TraesCS1D02G058900, was annotated within this region. TraesCS1D02G058900 encodes a receptor-like serine/threonine-protein kinase (STK), and a 6-bp deletion in exon 5 may confer the resistance to powdery mildew. Allele frequency analysis indicated that the STK allele with 6-bp deletion was only present in three landraces (Datoumai, Chiyacao [Pm24], and Hulutou) and was absent in all of the 353 Chinese modern cultivars and 147 foreign cultivars. These results demonstrate that PmDTM is mapped to the same locus as Pm24 and can be widely used to enhance powdery mildew resistance in wheat growing regions worldwide.