RACES OF PUCCINIA-GRAMINIS IN THE UNITED-STATES DURING 1990

Wheat stem rust overwintered in trace amounts from Louisiana to southern Alabama. No stem rust was found in fields of hard red spring or durum wheat cultivars. Race Pgt-QCCJ was the most common virulence combination, making up 67% of the 643 isolates from 240 collections. However, when only collections made from wheat were considered, the most common races, TPMK and QFCS, each made up 30% of the isolates. Of the isolates of race Pgt-QCCJ, 78% were recovered 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, and Wld-1. Oat stem rust was present in light amounts throughout most of the United States in 1990, and yield losses were negligible. Disease onset was a week 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-16, NA-5, and NA-10 made up 82, 10, 6, and 1%, respectively, of the isolates from the United States. No virulence to Pg-9, -13, -16, or -a was found in the 1990 oat stem rust population.