Races of Puccinia graminis in the United States and Mexico During 1986

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Abstract
Oat stem rust was present in light amounts throughout most of the United States in 1986, and yield losses were small except in central Minnesota and northern Wisconsin, where moderate losses occurred on late-planted oats. Disease development was generally more than a week later than the 40-yr average. The principal race in the United States and Mexico was NA-27, virulent on hosts with resistance genes Pg-1, -2, -3, -4, and -8. NA-27 constituted 89 and 100% of the isolates from the United States and Mexico, respectively. No virulence for Pg-a was found in oat stem rust. Wheat stem rust overwintered in trace amounts within an 80-km band from southern Texas to southern Alabama. Overwintering sites were found near Beeville and Victoria in southern Texas in early April. Additional overwintering sites were found in the Mississippi Valley into central Arkansas and along the Red River in southern Oklahoma in late April. Stem rust spread northward into Kansas and Nebraska by late May and into the northern Great Plains by mid-June. Although stem rust occurred on some hard red spring wheat cultivars resulting in slight losses, the recommended cultivars had adequate resistance and losses were nil. Race 15-TNM, virulent on plants with Sr17, was the most common virulence combination, making up 96% of the 1,582 isolates from 581 collections. The second most common race was 15-TNM, avirulent on Sr17, which made up 1% of the isolates. No virulence was found for wheat lines with "single" genes Sr13, 22, 24, 25, 26, 27, 29, 31, 32, 33, 37, Gt, and Wld-1.