RACES OF PUCCINIA-GRAMINIS IN THE UNITED-STATES AND MEXICO DURING 1983

Oat stem rust was present in trace amounts in the southern United States in 1983. Disease development was generally a week later than the 40-yr average. Losses were light throughout the USA. No isolates were obtained from Mexico. The principal race was NA-27, virulent on host genes Pg-1, -2, -3, -4, and -8, making up 88% of the isolates. No virulence was found in oat stem rust for host genes Pg-13, 16 or -a. Wheat stem rust was found in trace amounts in southern Texas in mid-March. Stem rust spread northward into the northern Great Plains by mid-June. Although moderate severities occurred in some hard red spring wheat fields, the cultivars had adequate resistance to prevent the massive inoculum levels of the mid-1950s and losses were minimal. Race 15-TNM, virulent on Sr17, was the most common virulence combination, making up 70% of the 1296 isolates from 466 collections. The second most common race was Sr17 avirulent on 15 TNM, which made up 24% of the isolates. No virulence was found on wheat lines with genes Sr13, 22, 24, 25, 26, 27, 29, 31, 32, 33, 37, Gt and Wld-1.