Trichoderma atroviride LU132 promotes plant growth but not induced systemic resistance to Plutella xylostella in oilseed rape

Several species of the fungus Trichoderma can promote plant health and are widely used as commercial biopesticides. Beneficial effects of this fungus are attributed to various mechanisms such as mycoparasitism, plant-growth promotion, increased stress tolerance and elicitation of induced systemic resistance against pathogens via jasmonic acid/ethylene-dependent pathways. Despite such well-established effects on pathogens, surprisingly little is known about the influence of Trichoderma on plant defences against herbivorous insects. This study investigated whether soil-supplementation of the established biocontrol agent Trichoderma atroviride LU132 affected the performance of oilseed rape (Brassica napus) and the development of Plutella xylostella caterpillars. Furthermore, induction and priming of defence-related phytohormones, genes and secondary metabolites by fungus and herbivore were assessed. Plants colonized by T. atroviride LU132 had significantly larger root and shoot biomass than controls. No effects of fungal inoculation were found on herbivore development. Leaf feeding of the herbivore induced higher jasmonic acid levels, but this was not influenced by fungal treatment. Similarly, the defence-related genes MYC2 and TPI were induced by herbivory but not primed or induced by T. atroviride. Expression of the gene PDF1.2 was repressed by herbivore feeding while no effects on the gene ACO and glucosinolates were observed. We conclude that T. atroviride LU132 has positive effects on the growth of oilseed but it does not enhance above-ground insect defences.