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

Strains of the tomato pathogen Cladosporium fulvum and the Brassica pa thogen Leptosphaeria maculans constitutively expressing beta-glucuroni dase were produced by cotransformation of a hygromycin-encoding vector pAN7-1 and a GUS encoding vector pNOM102. Their beta-glucuronidase ac tivity was used to detect histochemically the presence of fungal hypha e in host plant tissue. In addition, the beta-glucuronidase activity o f C. fulvum was used to quantify fungal biomass in the cotyledons of n ear-isogenic lines of tomato containing either no Cf resistance gene, or Cf-3, Cf-5, or Cf-9 resistance genes. Beta-Glucuronidase activity w as significantly reduced in incompatible interactions on Cf3, Cf5, and Cf9 plants as compared to the compatible interaction on CM. Histochem ical staining could also differentiate these interactions. These resul ts demonstrate that the production of beta-glucuronidase-expressing st rains of fungi provides a facile means to detect infection and quantif y biomass. Applications of this technique are discussed.