RACES OF PUCCINIA-GRAMINIS IN THE UNITED-STATES IN 1989

Oat stem rust was present in light amounts throughout most of the United States in 1989, and yield losses were nil. Disease onset was 1 mo later than the 40-yr average. The principal race in the United States was NA-27, virulent to resistance genes Pg-1, -2, -3, -4, and -8. NA-27, NA-5, and NA-16, respectively, made up 97, 1, and 1% of the isolates from the United States. No virulence was found for Pg-9, Pg-13, Pg-a, or Pg-16 in the 1989 oat stem rust population. Wheat stem rust overwintered in trace amounts from southern Texas to southern Alabama. A probable overwintering site on winter wheat was found in a northeastern North Dakota plot leeward of a shelterbelt. Stem rust inoculum spread northward, but little disease developed because of a severe drought throughout the central and northern Great Plains. No stem rust was found in fields of hard red spring or durum wheat cultivars. Race Pgt-TPM was the most common virulence combination, making up 53% of the 686 isolates from 247 collections. However, if only collections made from wheat were considered, it made up 73% of the isolates. Race Pgt-QCC made up 62% of the isolates from barley and 19% of all isolates. 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.