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Genetic variation and differentiation in global populations of the wheat leaf rust fungus, Puccinia triticina.

James Kolmer: USDA ARS

<div>The leaf rust pathogen, <em>Puccinia triticina</em> is common across all major wheat growing regions worldwide. Collections of <em>P. triticina</em> were obtained from common and durum wheat in North America, South America, Europe, South Africa, the Middle East, East Africa, Russia, Central Asia, China, Pakistan and New Zealand in order to determine the genetic diversity within each region and genetic relationship between regions. A total of 831 single uredinial isolates were characterized for virulence to isogenic lines of Thatcher wheat and for molecular genotype at 23 SSR loci. The isolates in East Africa and Europe were the most diverse for the average number of effective alleles per locus, while the populations in Russia and North America were the least diverse. The isolates in Europe and South America had the highest number of multilocus genotypes of 81 and 75, respectively, and were the most diverse for Shannon’s genotypic diversity. All populations had significantly higher levels of <em>H<sub>o</sub> </em>compared to <em>H<sub>e</sub></em> at individual SSR loci, and had highly significant values of <em>I</em><sub>a</sub> and r<sub>d</sub> which indicated clonal reproduction. Europe had the highest number of distinct SSR genotype groups with eight, and Russia had only two SSR groups. The populations in North America and South America; Russia and Central Asia; the Middle East and East Africa; were closely related for SSR genotype based on Nei’s genetic distance. Based on <em>k</em> means clustering and DAPC of SSR genotypes, isolates virulent to durum wheat were placed into a single separate genetic group, and isolates virulent to common wheat were placed into five groups. Twenty-seven SSR genotypes that were found in different continental regions, also had identical or similar virulence, which indicated historical and current migration of <em>P. triticina</em> worldwide.</div>