USE OF FUNGAL TRANSFORMANTS EXPRESSING BETA-GLUCURONIDASE ACTIVITY TO DETECT INFECTION AND MEASURE HYPHAL BIOMASS IN INFECTED-PLANT TISSUES

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 CM. 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.