Trichoderma harzianum T39 induces resistance against downy mildew by priming for defense without costs for grapevine

Downy mildew caused byPlasmopara viticolais one of the most destructive grapevine diseases world-wide. The biocontrol agentTrichoderma harzianumT39 (T39) has previously been shown to be an inducerof grapevine resistance, and we aimed at characterizing the molecular mechanisms activated by T39 andthe energy costs of the induced resistance in terms of plant growth. Here, we showed that T39 reduceddowny mildew severity on susceptible grapevines under controlled greenhouse conditions by a directmodulation of defense-related genes and the activation of priming for enhanced expression of thesegenes after pathogen inoculation. The stronger local than systemic modulation of defense-related genescorresponded to an higher local than systemic disease control in T39-treated plants. The activation of apriming state was confirmed by the absence of any negative effect of T39 on grapevine growth, shoot androot weight, leaf dimension and chlorophyll content, in contrast to benzothiadiazole (BTH) applications.Priming of defense gene expression was greater inT. harzianumT39- than in BTH-treated plants. Themodulation of marker genes suggested the involvement of jasmonic acid and ethylene signals in thedefense processes induced by T39, in contrast to the salicylic acid pathway activated by BTH. Theseresults offer a greater understanding of the mechanisms underlying the grapevine induced resistanceand indicate thatT. harzianumT39 can be used to control downy mildew without apparent costs forgrapevine growth. © 2011 Elsevier Inc. All rights reserved.