Presence of a sexual population of Puccinia graminisi f. sp. tritici in Georgia provides a hotspot for genotypic and phenotypic diversity

Authors: OLIVERA, PABLO - University Of Minnesota; SIKHARULIDZE, ZOYA - Batumi Shota Rustaveli State University; DUMBADZE, RUSUDAN - Batumi Shota Rustaveli State University; Szabo, Les; NEWCOMB, MARIA - University Of Minnesota; NATSARISHVILI, KETINO - Batumi Shota Rustaveli State University; Rouse, Matthew - Matt; Luster, Douglas - Doug; Jin, Yue

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2019
Publication Date: 10/30/2019
Citation: Olivera, P.D., Sikharulidze, Z., Dumbadze, R., Szabo, L.J., Newcomb, M., Natsarishvili, K., Rouse, M.N., Luster, D.G., Jin, Y. 2019. Presence of a sexual population of Puccinia graminisi f. sp. tritici in Georgia provides a hotspot for genotypic and phenotypic diversity. Phytopathology. 109(12):2152-2160. https://doi.org/10.1094/PHYTO-06-19-0186-R.
DOI: https://doi.org/10.1094/PHYTO-06-19-0186-R

Interpretive Summary: Wheat stem rust, caused by the rust fungus 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 occurs frequently and the alternate host, common barberry, is known to be present in an attempt to understand the potential roles that the alternate host may play in pathogen variations and disease epidemiology. A total of 118 single-pustule isolates were derived and evaluated on stem rust differential lines to determine the virulence phenotypes. Virulence analyses identified 23 races, many of which were detected for the first time. Unique virulence combinations were detected which, pose new challenges to breeding as many of these genes are being used in breeding for resistance to Ug99. Sixty-one isolates were genotyped using a custom SNP chip and identified 17 genotypes. The 2013 population was more diverse with 11 genotypes compared with 2014 and 2015 populations, five and three genotypes, respectively. The virulence and genotypic diversity observed strongly indicated that sexual recombination occurs in the Georgian P. graminis f. sp. tritici population and that Caucasus region of Eurasia may be an important source of new races. This information will be useful agricultural scientists in the understanding of stem rust pathogen variations and in wheat improvement for stem rust resistance.

Technical 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 118 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+Sr33+Sr35+Sr50 were detected. These virulence combinations pose new challenges to breeding as many of these genes are used in breeding for resistance to the Ug99 race group. Sixty-one isolates were genotyped using a custom SNP chip and identified 17 genotypes. The 2013 population was more diverse with 11 genotypes compared with 2014 and 2015 populations, five and three genotypes, respectively. The virulence and genotypic diversity observed strongly indicated that sexual recombination occurs in the Georgian P. graminis f. sp. tritici population and that Caucasus region of Eurasia may be an important source of new races.