Induction and accumulation of PR proteins activity during early stages of root colonization by the mycoparasite Trichoderma harzianum strain T-203

The biochemical nature of the interaction between the antagonistic fungus T richoderma 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 pene tration and colonization of the roots by T. harzianum were explored up to 7 2 h post-inoculation. Scanning electron microscopy (SEM) revealed typical f ungal structures previously associated with mycoparasitic interactions of I : harzianum strains during biological control. These included hyphal coilin g and appressoria formation. Compared to untreated control, cucumber roots treated with I: harzianum T-203 exhibited higher activities of chitinase (E C 3.2.1.14), beta -1,3-glucanase (EC 3.2.1.6), cellulase (EC 3.2.1.4) and p eroxidase (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 a cid (INA) displayed responses that were similar but not identical to those of plants inoculated with T. harzianum. In vivo staining of chitinase activ ity in fresh root sections allowed the localization of the activity in root s treated with either 2: harzianum T-203 or INA. The formation of fluoresce nt products mainly in intercellular spaces of the induced roots provided ev idence for the involvement of the plant defence system. In addition to its well-recognized mycoparasitic nature, it is suggested that Trichoderma's as sociation with roots reduce root disease through activation of the plant's defence response. (C) 2000 Editions scientifiques et medicales Elsevier SAS .