Use of β-Glucuronidase Activity to Quantify the Growth of Fusarium oxysporum f. sp radicis-lycopersici during Infection of Tomato

The beta-glucuronidase (gus) reporter gene was integrated into the phytopathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici (FORL) in a co-transformation experiment using the hygromycin B resistance (hph) gene as selective marker, which resulted in the generation of 10 mitotically stable transformants. One transformant, F30, was selected based on the results of prior detailed characterization of the 10 transformants for growth rate, conidia production and pathogenicity in comparison with the wild-type strain. A strong positive correlation was found between GUS activity and accumulated biomass of in vitro-grown fungus and therefore GUS activity was used to study fungal growth quantitatively in two tomato lines. Although a parallel increase in lesion development and GUS activity was noted for both tomato lines, a correlation between the GUS activity and disease progression was not always possible. Interestingly, the levels of GUS activity obtained for the more resistant line were higher than those obtained for the susceptible line, indicating that disease progression in tomato caused by FORL may not be related only to the amount of fungal biomass within the root tissue.