The Wheat Stem Rust ( Puccinia graminis f. sp. tritici ) Population from Washington Contains the Most Virulent Isolates Reported on Barley

• Published in: Plant disease Vol. 106; no. 1; p. 223
• Main Authors: Upadhaya, Arjun, Upadhaya, Sudha Gc, Brueggeman, Robert
• Format: Journal Article
• Language: English
• Published: United States 01-01-2022
• Subjects: Disease Resistance; Hordeum; Plant Diseases; Puccinia; Washington; Washington; RMRL; virulence; sexual populations; Puccinia graminis f. sp. tritici; Rpg1
• ISSN: 0191-2917
• DOI: 10.1094/PDIS-06-21-1195-RE

A diverse sexual population of wheat stem rust,
f. sp.
, exists in the Pacific Northwest region of the United States because of the natural presence of
spp. that serves as alternate hosts to complete its sexual life cycle. The region appears to be a center of stem rust diversity in North America where novel virulence gene combinations can emerge that could overcome deployed barley and wheat stem rust resistances. A total of 100 single pustule isolates derived from stem rust samples collected from barley in Eastern Washington during the 2019 growing season were assayed for virulence on the two known effective barley stem rust resistance genes/loci,
and the
-mediated resistance locus (RMRL) at the seedling stage. Interestingly, 99% of the
f. sp.
isolates assayed were virulent on barley variety Morex carrying the
gene, and 62% of the isolates were virulent on the variety Golden Promise transformant (H228.2c) that carries a single-copy insertion of the
gene from Morex and is more resistant than Morex to many
avirulent isolates. Also, 16% of the isolates were virulent on the near isogenic line HQ-1, which carries the RMRL introgression from the barley line Q21861 in the susceptible Harrington background. Alarmingly, 10% of the isolates were virulent on barley line Q21861, which contains both
and RMRL. Thus, we report on the first
f. sp.
isolates worldwide with virulence on both
and RMRL when stacked together, representing the most virulent
f. sp.
isolates reported on barley.