Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 1996
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. In years with the worst epidemics in the U.S., stem rust reduced wheat yields by more than 50 million bushels. Resistant varieties now protect the wheat crop, but there are many races of the stem rust fungus and no resistant variety is resistant to all of them. Therefore, it is necessary to survey the stem rust population in the United States annually to determine which races are present. In our 1995 survey, three races of wheat stem rust dominated the Great Plains population. None of these races is virulent on common spring wheat varieties grown in the Great Plains. Of 30 wheat lines tested, 16 with different resistance genes proved to be resistant to all of the stem rust races found in the 1995 survey. These lines can be used by wheat breeders in developing new stem rust resistant varieties. Our stem rust survey will provide early warning to wheat breeders if new virulent races appear in the Great Plains. It also will let them know which genes for resistance can give effective resistance to the new races. With sufficient early warning, wheat breeders will be able to develop new varieties with new resistance to prevent epidemics like those of the past that destroyed wheat worth hundreds of millions of dollars in a single year.
Technical Abstract: Wheat stem rust overwintered in southern Louisiana, southern Texas, southwest Georgia, northeastern Arkansas, and southwestern South Carolina in the winter of 1994-5. Wheat stem rust caused negligible yield losses in wheat in the U.S. Races Pgt-TPMK and QCCJ made up 39 and 31% of the isolates respectively, while 67% of the race TPMK were from only field isolates. Race Pgt-QCCJ was most common from barley, making up 93% from 47 collections. Six collections from H. jubatum yielded six isolates each of race QCCJ, QFCS, and one isolate of race TPMK. No virulence was found to wheat lines with genes Sr6,9b,13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, or Wdl-1. Oat stem rust overwintered in varietal plots at Beeville and Tempe , Texas and a field near San Antonio, Texas, and southern Louisiana.. Yield losses due to oat stem rust in 1995 were negligible. Race NA-27, virulent to Pg-1, 2, 3, 4, and 8, was again the predominant race in the United States comprising 82% of the 225 isolates from 80 collections. NA- 5, and NA-16 were the two other races identified from the United States, comprising 11 and 19% of the isolates. Only race NA-29 was found in four collections from Mexico.