Abstract
Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a re-emerging disease exemplified by recent epidemics caused by new virulent races. Understanding the sources and origins of genetic variations in the pathogen populations globally can facilitate the development of better strategies in disease management. We analyzed 68 wheat stem rust samples collected between 2013 and 2015 from Georgia where stem rust incidences are frequent and the alternate host, common barberry, is present. A total of 116 single-pustule isolates were derived and evaluated on stem rust differential lines to determine the virulence phenotypes and 23 races were identified, many of which were detected for the first time. Unique virulence combinations including, Sr22+Sr24 and Sr13b+Sr35+Sr37 were detected. These virulence combinations pose new challenges to breeding programs because many of these genes are used in breeding for resistance to the Ug99 race group. Sixty-one isolates were genotyped using a custom single-nucleotide polymorphism chip and 17 genotypes were identified. The 2013 isolates contained 11 multilocus genotypes compared with isolates of 2014 and 2015, with five and three genotypes, respectively. The higher levels of virulence and genotypic diversity observed in the 2013 samples strongly indicated that sexual recombination occurs in the Georgian P. graminis f. sp. tritici population, and that the Caucasus region of Eurasia may be an important source of new races.[Formula: see text] Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.
Highlights
Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a reemerging disease exemplified by recent epidemics caused by new virulent races
The higher levels of virulence and genotypic diversity observed in the 2013 samples strongly indicated that sexual recombination occurs in the Georgian P. graminis f. sp. tritici population, and that the Caucasus region of Eurasia may be an important source of new races
From the 90 P. graminis f. sp. tritici samples shipped to the U.S laboratories, 68 remained viable after transit from Georgia: 24/40 in 2013, 15/15 in 2015, and 29/35 in 2015
Summary
Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a reemerging disease exemplified by recent epidemics caused by new virulent races. Tritici, is a reemerging disease exemplified by recent epidemics caused by new virulent races. A total of 116 single-pustule isolates were derived and evaluated on stem rust differential lines to determine the virulence phenotypes and 23 races were identified, many of which were detected for the first time. These virulence combinations pose new challenges to breeding programs because many of these genes are used in breeding for resistance to the Ug99 race group. The occurrence and spread of Sr31virulent races in the Ug99 race group in East Africa (Newcomb et al 2016; Pretorius et al 2000; Singh et al 2015) and other races cause severe epidemics and localized outbreaks in Ethiopia (Olivera et al 2015), Europe Newcomb: University of Arizona, School of Plant Sciences, Maricopa, AZ 85138
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