Races of Puccinia graminis in the United States during 1996

Stem rust caused negligible yield losses in 1996 in the United States. Whea t stem rust was first found during the second week of April in a field of s oft red winter wheat southwest of Houston, Texas. Race Pgt-TPMK continues t o predominate, with 66% of 273 isolates from 100 collections. TPMK represen ted 76 and 63% of the isolates from wheat in fields and nurseries, respecti vely. Race QFCS was identified at a frequency of 12 and 29% from farm field s 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 isola tes of 27 collections, while TPMK consisted of 64% of the isolates. No viru lence 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, compri sing 91% of 93 isolates from 36 collections. NA-5 and NA-16 were the other two races identified, comprising 4% each.