Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 18, 1995
Publication Date: N/A
Interpretive Summary: Stem rust caused by the fungus Puccinia graminis affects small grain crops, causing severe damage to susceptible varieties of wheat, barley, and oat. Before resistant wheat varieties were developed, stem rust epidemics often swept north from Texas, where the fungus survives the winter, causing heavy yield losses in central and northern plains states. Barley, which is grown mainly in the northern plains, is also vulnerable to stem rust, because rust races that attack wheat may also attack barley. Resistance to stem rust is not universally effective against all races of the fungus. It is essential to survey rust populations to determine which races are present and where they occur in the USA each year. In our 1993 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. Even though stem rust was severe in fields near Houston, TX, and in southwestern Arkansas, stem rust caused no appreciable loss in the main wheat-growing areas of 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. Race pgt-QCCJ, which attacks all barley varieties currently grown in the USA, was common in 1993, but losses to stem rust in barley were light because early rust infections of race pgt-QCCJ in the South were light and the cool weather delayed rust buildup and spread to the North. Very little oat stem rust occurred except in the South in 1993.
Technical Abstract: Wheat stem rust overwintered in southern Texas, southern Louisiana, and southern Georgia. Yield losses in wheat to stem rust were traces, but several ha southwest of Houston were destroyed. Race Pgt-TPMK was the most common race overall, making up 61% of the 895 isolates from 311 collections. From Hordeum spp., 112 collections were made, in which the most common race was Pgt-QCCJ, comprising 56% of the isolates. Eighty-eight percent of the isolates of QCCJ were from cultivated barley and 56% of all isolates from cultivated barley were race QCCJ. No virulence was found to wheat lines with "single" genes SR13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 33, 37, Gt, or Wld-1. Little oat stem rust overwintered in the southern states in 1993. Yield losses in 1993 were negligible. Race NA-27, virulence to Pg-1, -2, -3, -4, and -8 was again the predominant race in the United States comprising 81% of the 93 isolates from 33 collections. NA-5, and NA-10 were the other races isolated, comprising 9 and 11% of the population, respectively. No virulence to Pg-9, -13, -16, or -a was found in the 1993 oat stem rust population.