Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 3, 1995
Publication Date: N/A
Interpretive Summary: Stem rust caused by the fungus Puccinia graminis can cause severe damage to susceptible varieties of wheat, barley, and oat. Epidemics of wheat stem rust in the Great Plains typically start in winter wheat in Texas and spread north as far as the Prairie Provinces of Canada each year. To protect cereal crops from stem rust it is necessary to breed rust resistant varieties. It is also necessary to survey rust populations to determine which races are present and where they occur in the USA each year. The reason is that resistance against some races of stem rust may not be effective against other races. This is especially important for wheat, because the very extensive wheat acreage in the Great Plains makes the area vulnerable to epidemics. In our 1994 survey, three races of wheat stem rust dominated the Great Plains population. None of these races is virulent on common spring wheat varieties in the Great Plains. Of 30 wheat lines tested, 14 with different resistance genes were resistant to all races found in 1993. These genes may provide resistance against new races. One race, pgt-QCCJ, made up 90% of the stem rust samples collected from barley. This race can overcome the resistance of all com- mercially grown barley varieties in the U.S. Stem rust damage to barley was not heavy in 1994, because the epidemic started late. Also, there was little stem rust damage to oats in 1994. The limited oat and barley acreage in the central Great Plains reduces rust spread to the north and limits epidemics on those crops.
Technical Abstract: Wheat stem rust overwintered in southern Louisiana and Texas. Wheat stem rust caused negligible yield losses in wheat in the U.S., and less than 1% loss in North Dakota. Race Pgt-TPMK was the most common race on wheat, making up 39% from 51 collections, while Pgt- QCCJ was most common from barley, making up 90% from 38 collections. Four collections from H. jubatum yielded six isolates of race TMPK, four isolates of race QCCJ, and one each of races RKQQ and RTQQ. No virulence was found to wheat lines with "single" genes Sr13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, or Wdl-1. No oat stem rust was found in late March in southern Texas along the Gulf Coast and Florida. Yield losses in 1944 were negligible. Race NA27, virulent to Pg-1, 2, 3, 4, and 8, was again the predominant race in the United States comprising 87% of the 119 isolated from 41 collections. NA-5, and NA-16 were the two other races identified from the United States, comprising 3 and 10% of the races. Only race NA-29 was identified from 50 collections from Central Mexico.