Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 29, 1992
Publication Date: N/A
Interpretive Summary: Annual, national surveys of wheat and oat stem rust fungi to monitor changes in virulence are conducted at the Cereal Rust Lab. When a race with a new virulence gene or combination of virulence genes is detected, it is saved and used in selecting new cultivars with resistance to the new race as well as to previously identified races. For wheat stem rust, which also attacks barley, race Pgt- QCCJ was the most common race in 1991, comprising 68% of the isolates. Sixty-seven percent of the isolates of race Pgt-QCCJ were from cultivated barley. If only collections made from wheat were considered, the most common races were QCCJ, TPMK and QFCS, comprising 38, 36 and 25% of the isolates, respectively. In 1991, no major shift in races occurred in oat stem rust and no new virulences were detected.
Technical Abstract: Stem rust has been a major disease of wheat and oat crops in the northern Great Plains since 1878. Disease incidence and severity were observed along a 22,000 km survey route. Single pustule isolates from survey collections were inoculated to standard differential host lines possessing a single resistance gene. Wheat stem rust overwintered in southern Texas, southern Louisianaand southwestern Georgia. Yield losses due to stem rust in wheat and barley were light; however, losses up to 10% occurred in some barley fields in east central North Dakota. Race Pgt-QCCJ was the most common virulence combination making up 68% of the 1279 isolates from 487 collections. However, if only collections made from wheat were considered, the most common races were QCCJ, TPMK and QFCS, comprising 38, 36 and 25% of the isolates, respectively. Seventy-eight percent of the isolates of race Pgt-QCCJ were from barley. No virulence was found for wheat lines with "single" genes Sr13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, or Wld-1. Oat stem rust was present in light amounts occurring only in the Gulf Coast area, Northern Plains, and in California, which is an isolated population. Yield losses in 1991 were negligible. The principal race in the United States was NA-27, virulent to resistance genes Pg-1, -2, -3, -4, and -8. NA-27, NA-16, and NA-5 made up 94, 4, and 2% of the isolates from the U.S., respectively. No virulence was found for Pg-9, -13, -16, or -a in the 1991 oat stem rust population.