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ARS Home » Pacific West Area » Pullman, Washington » WHGQ » Research » Publications at this Location » Publication #332984
Title: Changes of races and virulence genes of Pucccinia striiformis f. sp. tritici, the wheat stripe rust pathogen, in the United States from 1968 to 2009

Author
item LIU, TINGLAN - Washington State University
item WAN, ANMIN - Washington State University
item LIU, DENGCAI - Sichuan University
item Chen, Xianming

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2017
Publication Date: 7/11/2017
Citation: Liu, T., Wan, A., Liu, D., Chen, X. 2017. Changes of races and virulence genes of Pucccinia striiformis f. sp. tritici, the wheat stripe rust pathogen, in the United States from 1968 to 2009. Plant Disease. 101(8):1522-1532.

Interpretive Summary: The rapid changes of virulences in the stripe rust pathogen can circumvent resistance in wheat varieties and cause severe epidemics. Because the pathogen races have been identified in the United States using different wheat varietiess in different time periods, it is difficulty to make direct comparison of the current population with historical populations. The objective of this study was to characterize historical populations with the recently established set of wheat single-gene differentials. From 908 isolates collected from 1968 to 2009 in the United States, 171 races were identified. Virulences to the 18 Yr genes, except Yr5 and Yr15, were detected but in different periods, and most virulences increased in frequency over time. Some virulences appeared much earlier than previously thought. Positive and negative associations were detected between virulences. The 171 races were clustered into two major virulence clusters and further grouped into eight virulence groups. The virulence groups differ in the mean number of virulences, common virulences, and common avirulences, as well as in different periods of development. About 74% of the races were presumably evolved from previously existing races through a single- or double-step mutations, whereas the remaining 26% of the races might appear through introduction and/or somatic recombination. The continual information on virulences and races of the pathogen is useful for understanding the evolution of the pathogen and for breeding wheat varieties with resistance to stripe rust.

Technical Abstract: Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a serious disease of wheat in the world. The obligate biotrophic fungal pathogen changes its virulence rapidly, which can circumvent resistance in wheat cultivars and cause severe epidemics. Because Pst races have been identified in the United States using different wheat genotypes in different time periods, it is difficulty to make direct comparison of the current population with historical populations. The objective of this study was to characterize historical populations with 18 Yr single-gene lines that are currently used to differentiate Pst races in order to understanding virulence and race dynamics of the pathogen. From 908 Pst isolates collected from 1968 to 2009 in the United States, 171 races were identified. Virulences to the 18 Yr genes, except Yr5 and Yr15, were detected but in different periods, and most virulences increased in frequency over time. Some virulences such as those to Yr17, Yr27, Yr32, Yr43, Yr44, YrTr1, and YrExp2 appeared much earlier than previously thought. Positive and negative associations were detected between virulences. The 171 races were clustered into two major virulence clusters (VCs) and further grouped into eight virulence groups (VGs). The eight VGs differ in the mean number of virulences, common virulences, and common avirulences. Three VGs (VG1, VG2, and VG5) in VC1 were detected in all periods from 1968 to 2009; VG4 in VC1 was detected in the periods from 1978 to 2009; VG3 in VC1 and VG6 in VC2 were detected only after the year 2000; and VG7 and VG8 in VG2 were detected after 1998 and 1993, respectively. About 127 (74%) of the races were presumably evolved from previously existing races through a single- or double-step mutations, whereas the remaining 44 (26%) races might appear through introduction and/or somatic recombination. The continual information on virulences and races in the Pst populations is useful for understanding the evolution of the pathogen and for breeding wheat cultivars with effective resistance to stripe rust.