EFFECT OF TRICHODERMA-HARZIANUM ON BOTRYTIS-CINEREA PATHOGENICITY

Germination and germ-tube elongation of conidia of the pathogen Botryt is cinerea on bean leaves were reduced in the presence of the biocontr ol agent Trichoderma harzianum T39. A reduction of 20 to 50% in germ-t ube biomass was observed 20 h after inoculation. This reduction in ger mination did not result in complete prevention of disease development on the leaves. One day after inoculation, disease severity on leaves i nfected by the pathogen with and without the biocontrol agent was simi lar (similar to 10% necrotic area). Subsequently, the disease develope d rapidly in the control leaves and caused almost complete necrosis, w hereas in the presence of T. harzianum T39 the necrotic area reached o nly similar to 50% of the leaf surface. The production of pectin-degra ding enzymes by B. cinerea was measured up to 4 days after inoculation . Up to 1.3 enzyme units of polygalacturonase (PG), 9 microequivalents of NaOH, which express the activity of pectin methyl esterase (PME), and up to 1.5 units of pectate lyase (PL) were detected on bean leaves . Under the same conditions, the biocontrol agent, T. harzianum T39, d id not produce any of these enzymes. On leaves infected with B. cinere a in the presence of the biocontrol agent, the activity of the pathoge n's PG was reduced by 40 to 83%. This was reflected on an activity gel by the faintness of these PG isoenzymes and the delay in their appear ance. An up to 100% reduction in PME activity and a similar to 30% red uction in PL activity also were recorded. We suggest that T. harzianum T39 acts by reducing the enzyme activities of the pathogen. An indire ct effect of enhancing the defense mechanism of the host plant is disc ussed.