Role of uronic acids present in phytopathogenic fungi as inducers of polygalacturonases during autolysis

The presence of uronic acids in the culture fluid and mycelium of the fungi: Alternaria alternata, Botrytis cinerea, Drechslera halodes, Fusarium culmorum, Fusarium oxysporum, Monilinia fructigena, Mucor mucedo, Rhizopus stolonifer and Trichoderma hamatum was detected and quantified. In these fungi the concentration of uronic acids increased during the growth phase and the maximal concentrations were found at the end of the growth phase or onset of autolysis both in the mycelium as well as in the culture fluid. The uronic acids were metabolized during the first days of autolysis decreasing to constant levels until the end of the autolytic period studied.The variations in the activity of polygalacturonase and polymethylgalacturonase present in the culture fluid were determined at the onset and during autolysis in these fungi. These enzymic activities were found in the culture fluid of these fungi, with exception of M. rouxii, and they showed an increasing activity in the first days of autolysis and later a slight increase or decrease was observed. The presence of uronic acids in these phytopathogenic or saprophytic fungi and the low levels detected during autolysis could be related to the induction of pectic enzymes and the pathogenicity of these fungi.