Races of Puccinia graminis in the United States During 1997 and 1998.

Wheat stem rust caused negligible yield losses in 1997 and 1998. Overwintering sites were found in central and east-central Louisiana in 1997, and in northwestern Florida, northeastern Louisiana, and central Texas in 1998. Race Pgt-TPMK predominated in 1997 with 69% of 100 isolates with race RCRS next at 11%. In 1998, race RCRS predominated with 55% of 132 isolates, and TPMK occurred at 10%. Race QFCS occurred at 8% in 1997 and 31% in 1998. Races QCCS and QTHJ were found in 1997, and races QFBS, RKMQ, RKQQ, and RCMS were found in 1998. Race QCCJ, virulent to barley with the Rpg1 gene for stem rust resistance, was not found from wheat in 1997 or 1998. No virulence was found to wheat lines with Sr 13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 37, Gt, or Wld-1. Oat stem rust was found earlier in 1997 than 1998, but was more widespread in 1998. Race NA27, virulent to Pg-1, -2, -3, -4, and -8, was the predominant race in the United States in 1997 (79% of 116 isolates) and again in 1998 (79% of 116 isolates). NA16, virulent to Pg-1, -3, and -8, was found in the south (1997 and 1998), and NA5, virulent to Pg-2 and -15, and NA10, virulent to Pg-2, -3, and -15, were found in the west (1997).