Research Notes Use of Fungal Transformants Expressing Beta-Glucuronidase Activity to Detect Infection and Measure Hyphal Biomass in Infected Plant Tissues. Richard P. Oliver. Norwich Molecular Plant Pathology Group, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ England. Mark L. Farman(1), Jonathan D. G. Jones(2), and Kim E. Hammond-Kosack(2). (1)Norwich Molecular Plant Pathology Group, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ England; (2)Sainsbury Laboratory, John Innes Centre for Plant Science Research, Colney Lane, Norwich NR4 7UH England.. MPMI 6:521-525. Accepted 31 March 1993. Copyright 1993 The American Phytopathological Society.

Strains of the tomato pathogen Cladosporium fulvum and the Brassica pathogen Leptosphaeria maculans constitutively expressing Beta-glucuronidase were produced by cotransformation of a hygromycin-encoding vector pAN7-1 and a GUS encoding vector pNOM102. Their Beta-glucuronidase activity was used to detect histochemically the presence of fungal hyphae in host plant tissue. In addition, the Beta-glucuronidase activity of C. fulvum was used to quantify fungal biomass in the cotyledons of near-isogenic lines of tomato containing either no Cf resistance gene, or Cf-3, Cf-5, or Cf-9 resistance genes. Beta-Glucuronidase activity was significantly reduced in incompatible interactions on Cf3, Cf5, and Cf9 plants as compared to the compatible interaction on Cf0. Histochemical staining could also differentiate these interactions. These results demonstrate that the production of Beta-glucuronidase-expressing strains of fungi provides a facile means to detect infection and quantify biomass. Applications of this technique are discussed.