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Identifying Wheat Genotypes Resistant to Eyespot Disease with a ?-Glucuronidase-Transformed Strain of Pseudocercosporella herpotrichoides. Robert C. de la Peņa, Graduate student, Department of Plant Pathology, Washington State University, Pullman 99164-6430; Timothy D. Murray, associate professor, Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 84:972-977. Accepted for publication 14 June 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-972.

Resistance to Pseudocercosporella herpotrichoides in wheat was determined by inoculating 2-wk-old seedlings with a transformed strain of the pathogen that constitutively expresses β-glucuronidase (GUS) and measuring disease development with a GUS enzyme assay, visual disease scoring, and an enzyme-linked immunosorbent assay (ELISA). Differences among resistant and susceptible genotypes were apparent 2 wk after inoculation; however, the greatest differences among resistant and susceptible genotypes occurred 4- to 6-wk and 6- to 8-wk after inoculation for the GUS assay and visual disease ratings, respectively. ELISA did not differentiate among resistant genotypes at any sample date in this study. Values obtained with the GUS system provided the largest differences among and between resistant and susceptible genotypes. In addition, the GUS system has the advantage of being objective, faster, and more sensitive than visual disease ratings.