Races of Puccinia graminis in the United States During 1996

Stem rust caused negligible yield losses in 1996 in the United States. Wheat stem rust was first found during the second week of April in a field of soft red winter wheat southwest of Houston, Texas. Race Pgt-TPMK continues to predominate, with 66% of 273 isolates from 100 collections. TPMK represented 76 and 63% of the isolates from wheat in fields and nurseries, respectively. Race QFCS was identified at a frequency of 12 and 29% from farm fields and nurseries, respectively, and 26% overall. Eight other races consisted of 3% or less of the isolates. From barley, race QCCJ, virulent to the Rpg-1 gene for resistance to stem rust, was identified in only 12% of 77 isolates of 27 collections, while TPMK consisted of 64% of the isolates. No virulence was found to wheat lines with genes Sr9b, 13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 37, Gt, or Wld-1. Oat stem rust was first found in late April in southern Louisiana and central Texas. Race NA-27, virulent to Pg-1, -2, -3, -4, and -8, was again the predominant race in the United States, comprising 91% of 93 isolates from 36 collections. NA-5 and NA-16 were the other two races identified, comprising 4% each.