Evaluation of induction of systemic resistance in pepper plants (Capsicum annuum) to Phytophthora capsici using Trichoderma harzianum and its relation with capsidiol accumulation

The effect of pepper seed and root treatments with Trichoderma harzianum sp ores on necrosis caused in stems by Phytophthora capsici inoculation and on the course of capsidiol accumulation in the inoculated sites were studied. The results indicate that seed treatments significantly reduced stem necro sis, which fell by nearly a half compared with the values observed in plant s grown from non-treated seeds. Necrosis was also reduced in plants whose r oots were drenched with various doses of T. harzianum spores, although the extent of necrosis was not correlated with the dose used. Attempted isolati on of P. capsici and I: harzianum from the zones immediately contiguous wit h the necrotic zones revealed the presence of the former but not of the lat ter, suggesting that there was no direct contact between them in the zones of isolation, which means that there was no competition for space. The perc entage of P. capsici isolated 9 days after inoculation was greater in non-t reated inoculated plants than in treated inoculated plants. These results s uggest that T. harzianum, introduced into the subterranean part of the plan t, induces a systemic defense response against P. capsici in the upper part of the plant. Analysis of capsidiol in the stems of treated inoculated pla nts by the end of the sixth day after inoculation, revealed that its concen tration was more than seven-fold greater than in non-treated and inoculated plants, while after 9 days, the concentration of capsidiol decreased in th e treated inoculated plants and increased in the non-treated inoculated pla nts. The high concentration of capsidiol detected in treated and inoculated stems after 6 days might be one of the contributing factors, but not neces sarily the main factor, in delaying lesion development in the stems of pepp er plants.