Induction and accumulation of PR proteins activityduring early stages of root colonizationby the mycoparasite Trichoderma harzianum strain T-203

The biochemical nature of the interaction between the antagonistic fungus Trichoderma harzianum strain T-203 and cucumber roots was studied during the early stages of root colonization by the fungus. Pathogenesis related (PR) proteins of the plant and enzyme activity of the fungus following the penetration and colonization of the roots by T. harzianum were explored up to 72 h post-inoculation. Scanning electron microscopy (SEM) revealed typical fungal structures previously associated with mycoparasitic interactions of T. harzianum strains during biological control. These included hyphal coiling and appressoria formation. Compared to untreated control, cucumber roots treated with T. harzianum T-203 exhibited higher activities of chitinase (EC 3.2.1.14), β-1,3-glucanase (EC 3.2.1.6), cellulase (EC 3.2.1.4) and peroxidase (EC 1.11.1.7), up to 72 h post-inoculation. Plants treated with a chemical inducer of the plant defence response, 2,6-dichloroisonicotinic acid (INA) displayed responses that were similar but not identical to those of plants inoculated with T. harzianum. In vivo staining of chitinase activity in fresh root sections allowed the localization of the activity in roots treated with either T. harzianum T-203 or INA. The formation of fluorescent products mainly in intercellular spaces of the induced roots provided evidence for the involvement of the plant defence system. In addition to its well-recognized mycoparasitic nature, it is suggested that Trichoderma’s association with roots reduce root disease through activation of the plant’s defence response.