Field samples of Puccinia recondita f. sp. tritici, collected from four wheat-growing regions in Nebraska in 1995 and from three in 1996, were characterized for virulence. Twenty virulence phenotypes were identified in 1995 and 18 in 1996. Virulence phenotypes MBR-10,18 (virulent on Lr genes, 1, 3, 3ka, 10, 11, 18, and 30) and MDR-10,18 (virulent on Lr genes 1, 3, 3ka, 10, 11, 18, 24, and 30) were the most prevalent, with each phenotype comprising 21.6% of the isolates characterized in 1995. Of the 1995 isolates, 24% were virulent on 10 or more host genes. No virulence to Lr16 and Lr17 was detected. In 1996, virulence phenotype MBR-10,18 was the most prevalent and comprised 20.5% of the isolates characterized. Of the 1996 isolates, 33% were virulent on 10 or more host genes. All isolates in both years were virulent on Lr1, Lr3, and Lr10. New virulence phenotypes were detected in 1996 that were not detected in 1995. In 1996, virulence was more frequent on Lr2a, Lr16, and Lr17 and less frequent on Lr3ka, Lr18, Lr24, Lr26, and Lr30. The number of isolates virulent on Lr24 and Lr26 has decreased from 83 and 53%, respectively, in 1992, to 34 and 1%, respectively, in 1996
