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Trichoderma harzianum and Glomus intraradices Modify the Hormone Disruption Induced by Fusarium oxysporum Infection in Melon Plants

The plant hormones salicylic acid (SA), jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA) are known to play crucial roles in plant disease and pest resistance. Changes in the concentrations of these plant hormones in melon plant shoots, as a consequence of the interaction between the plant, the pathogen Fusarium oxysporum, the antagonistic microorganism Trichoderma harzianum, and the arbuscular mycorrhizal fungus Glomus intraradices were investigated. Attack by F. oxysporum activated a defensive response in the plant, mediated by the plant hormones SA, JA, ET, and ABA, similar to the one produced by T. harzianum. When inoculated with the pathogen, both T. harzianum and G. intraradices attenuated the plant response mediated by the hormones ABA and ET elicited by the pathogen attack. T. harzianum was also able to attenuate the SA-mediated response. In the three-way interaction (F. oxysporum--T. harzianum--G. intraradices), although a synergistic effect in reducing disease incidence was found, no synergistic effect on the modulation of the hormone disruption induced by the pathogen was observed. These results suggest that the induction of plant basal resistance and the attenuation of the hormonal disruption caused by F. oxysporum are both mechanisms by which T. harzianum can control Fusarium wilt in melon plants; while the mechanisms involving G. intraradices seem to be independent of SA and JA signaling.