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Research Project: Genetic Improvement of Small Grains for Biotic and Abiotic Stress Tolerance and Characterization of Pathogen Populations

Location: Plant Science Research

Title: Differentiation among Israeli Blumeria graminis f. sp. tritici isolates originating from wild vs. domesticated Triticum species

Author
item BEN DAVID, ROI - Volcani Center (ARO)
item Cowger, Christina
item Parks, Wesley
item DINOOR, AMOS - Volcani Center (ARO)
item KOSMAN, EVSEY - Tel Aviv University
item WICKER, THOMAS - University Of Zurich
item KELLER, BEAT - University Of Zurich

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2016
Publication Date: 6/8/2016
Citation: Ben David, R., Cowger, C., Parks, W.R., Dinoor, A., Kosman, E., Wicker, T., Keller, B. 2016. Differentiation among Israeli Blumeria graminis f. sp. tritici isolates originating from wild vs. domesticated Triticum species. Phytopathology. http://dx.doi.org/10.1094/PHYTO-07-15-0177-R.

Interpretive Summary: Israel is a center of diversity of domesticated wheat species (Triticum aestivum and T. durum) and their wild relatives, including wild emmer wheat (T. dicoccoides). We studied 61 strains of the powdery mildew pathogen, Blumeria graminis f. sp. tritici (Bgt) that were collected from the three host species (common wheat, durum wheat, or wild emmer wheat) in four regions of Israel. We measured the strains’ ability to cause disease on wheat lines containing different mildew resistance genes, and we also assessed similarity among the strains based on molecular markers. We found no difference among the strains based on their geographic region of origin. However, all our tests showed that mildew strains collected from domesticated wheat were different from strains originating from wild emmer wheat. Analyses of migration showed that the mildew strains from common wheat and durum wheat formed a single, randomly mating population. We also found that there is one-way migration of strains from the mildew population on domestic wheat to the mildew population on wild emmer at a rate of five to six individuals per generation. In general, the “wild” and “domestic” mildew populations were distinguished both by which resistance genes they could overcome and by molecular markers. The results suggest that in its center of origin, wheat powdery mildew is in the process of diverging into separate emmer and domesticated wheat populations.

Technical Abstract: Israel and its vicinity constitute a center of diversity of domesticated wheat species (Triticum aestivum and T. durum) and their sympatrically growing wild relatives, including wild emmer wheat (T. dicoccoides). The present study explored differentiation within the forma specialis of their obligate powdery mildew pathogen, Blumeria graminis f. sp. tritici (Bgt). A total of 61 Bgt isolates was collected from the three host species in four geographic regions of Israel. Genetic relatedness of the isolates was characterized using both virulence patterns on 38 wheat lines (including 21 Pm differentials) and presumptively neutral molecular markers (simple-sequence repeats, or SSRs, and single-nucleotide polymorphisms, or SNPs). No differentiation by geographic region was found among the isolates. All assays divided the Bgt collection into two distinct groups, one group containing isolates from domesticated hosts (T. durum and T. aestivum) and the other comprised of isolates from wild emmer wheat. Analyses of migration indicated that the mildew populations from T. durum and T. aestivum were panmictic. One-way migration was detected from the domestic-wheat Bgt population to the wild emmer Bgt population at a rate of five to six migrants per generation. While wild and domestic Bgt populations clustered separately by virulence and SSR markers, there was some overlap, likely based on gene flow from cultivated wheat fields to natural populations. Overall, however, the results indicate that in its center of origin, the wheat forma specialis of Blumeria graminis is in the process of diverging into emmer and domesticated wheat populations.