Virulence of Puccinia recondita and Cultivar Relationships in Texas from 1985 to 1987. D. Marshall, Texas Agricultural Experiment Station, Texas A&M University Research and Extension Center, 17360 Coit Road, Dallas 75252. . Plant Dis. 73:306-308. Accepted for publication 2 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0306.

Texas was divided into eight agroecological areas of adaptation for wheat leaf rust. Those areas were the High Plains, Rolling Plains, Blacklands, Gulf Coast, east, southwest, south-central, and south Texas. Isolates of Puccinia recondita were collected in each area over a 2-yr period. The isolates were characterized into 39 virulence/avirulence phenotypes, which were grouped into 10 Unified Numeration (UN) races. The most prevalent race was UN 5, which made up 43% of the 1,065 isolates collected. During 1985–1986, 52% of the isolates sampled were virulent to Lr16, whereas only 18% were virulent to Lr16 during 1986–1987. The decline in the percentage of isolates virulent to Lr16 paralleled a decrease in plantings of the cultivar Probrand 812. Races carrying virulence to Lr24 became widespread throughout Texas during 1986–1987, following an increase in acreage of cultivars carrying the Lr24 gene. Races carrying virulence to Lr3, 11, 18 and Lr3, 9, 3ka in race UN2, and Lr1, 2a, 2c, 10, 17 in race UN 9 were isolated for the first time from Texas. No correlation was found between the number of virulence genes and the frequency of races.