<i>PRODUCTION OF PR PROTEINS DURING THE INDUCTION OF RESISTANCE TO PHYTOPHTHORA CAPSICI IN PEPPER (CAPSICUM ANNUUM L.) PLANTS TREATED WITH TRICHODERMA HARZIANUM</i>

Abstract

We evaluate the defensive reaction of pepper plants after inoculating the stems with the pathogen Phytophthora capsici and treating the roots with the antagonist Trichoderma harzianum. Treating the seeds with T. harzianum increases the germination percentage and dry weight of the seedlings. The hyphae of the antagonist colonise the roots and the rhizopsphere of the seedlings grown from treated seeds although the fungus does not grow in the aerial part of the plants. Infection of the stems with the pathogen produces a hypersensitivity reaction but necrosis is slowed down in plants treated with the antagonist T. harzianum, as a result of induced resistance. The addition of the antagonist T. harzianum to plants inoculated with P. capsici produces a defensive reaction involving the production of proteins showing peroxidase activity. The increase in activity affects both constitutive enzymes and those synthesised “de novo”, although the increase in activity detected in control plants is due to the effect of the wound rather than to the treatment since it does not increase with time. Treatment with T. harzianum induces a systemic reaction in the leaves, which is resolved by the production of PR proteins with peroxidase activity, even though the leaves are not affected by the antagonist or by the pathogen. These PR peroxidases are basic (p.I. 7.2 and 8.7) and are only detected in leaves treated with live T. Harzianum 96 hours after inoculation. Increased peroxidase activity is also observed in roots and the production of a PR protein is observed both at 24 and 96 hours. This isoenzyme is acidic (p.I. 4.3) and seems to be produced as a result of treatment with both live and autoclaved T. harzianum, but does not appear in the control or in the roots treated with water-peptone. This means that the elicitor is a component of the mycelium of the antagonist fungus, which provokes a defensive reaction involving the formation of peroxidases. The production of PR-proteins with peroxidase activity presumably forms part of the hypersensitive defence mechanism of pepper plants and would be responsible for the induction of the resistance developed by the plant after treatment with the antagonist T. harzianum and infection by the pathogen.