Trichoderma harzianum enhances tomato indirect defense against aphids

Abstract

Many fungal root symbionts of the genus Trichoderma are well-known for their beneficial effects on agronomic performance and protection against plant pathogens; moreover, they may enhance protection from insect pests, by triggering plant resistance mechanisms. Defense barriers against insects are induced by the activation of metabolic pathways involved in the production of defense-related plant compounds, either directly active against herbivore insects, or exerting an indirect effect, by increasing the attraction of herbivore natural enemies. In a model system composed of the tomato plant, the aphid Macrosiphum euphorbiae and the parasitoid Aphidius ervi, plant metabolic changes induced by Trichoderma harzianum and their effects on higher trophic levels have been assessed. T. harzianum T22 treatments induce a primed state that upon aphid attacks leads to an increased attraction of aphid parasitoids, mediated by the enhanced production of volatile organic compounds (VOCs) that are known to induce Aphidius ervi flight. Transcriptome sequencing of T22-treated plants infested by aphids showed a remarkable upregulation of genes involved in terpenoids biosynthesis and salicylic acid pathway, which are consistent with the observed flight response of A. ervi and the VOC bouquet profile underlying this behavioral response.

The Beneficial Endophytic Fungus Fusariumsolani Strain K Alters Tomato Responses Against Spider Mites to the Benefit of the Plant

“…Very little is known about the effects of endophytic fungi on plant volatile production [mainly focused on Trichoderma species, e.g., Battaglia et al (2013) , Coppola et al (2017) , Contreras-Cornejo et al (2018) ] and to the best of our knowledge, no previous study has ever explored how plant colonization by an endophytic fungus mediates the volatile-regulated attraction of insect predators to spider mite-infested plants. We herein show that the generalist predator M. pygmaeus was attracted to FsK-colonized plants irrespectively of the presence of spider mites (Figure 8 ).…”

“…Indeed, certain root endophytic fungi have been shown to increase the expression of defense-related genes and the production of secondary metabolites that may be relevant to plant defense ( Pieterse et al, 2014 ). In addition, a few studies involving endophytic fungi have reported negative effects on above ground herbivores thus enhancing their potent role in plant resistance to biotic stressors ( Jallow et al, 2004 ; Jaber and Vidal, 2009 , 2010 ; Muvea et al, 2014 ; Coppola et al, 2017 ; Contreras-Cornejo et al, 2018 ). Nevertheless, our understanding of endophytic fungi – plant – herbivore interactions is still at its infancy thus calling for more empirical studies on the significance of horizontally transmitted endophytes in plant–herbivore interactions ( Gan et al, 2017 ).…”

Trichoderma gamsii affected herbivore feeding behaviour on Arabidopsis thaliana by modifying the leaf metabolome and phytohormones

“…The Trichoderma ‐induced resistance in plants leads to physiological and biochemical changes including enhanced defence enzymatic activity, upregulation of defence‐related genes, and changes in metabolic profiles (Mastouri et al ., 2010; Contreras‐Cornejo et al ., 2011; Carreras‐Villasenor et al ., 2012). A recent study showed that Trichoderma harzianum T22 can enhance the production of volatile organic compounds (VOCs) in tomato leading to an increased attractiveness towards aphid parasitoids (Coppola et al ., 2017). A similar study showed that T. atroviride triggers maize defences against the insect herbivore S. frugiperda by the increased emission of volatile terpenes and accumulation of jasmonic acid (JA) (Contreras‐Cornejo et al ., 2018).…”

The promises and challenges of research on plant–insect–microbe interactions

“…Coppola et al . () bring another compelling evidence whereby Trichoderma hazarnium , a fungal root symbiont commonly used in biological control, reinforces parasitoid attraction towards aphid‐infested tomato plants. Interestingly, plants infested by aphids and associated with Trichoderma showed enhanced production and release of volatiles known to attract parasitoids, which very likely accounted for observed differences in flight behavior.…”

“…Another important challenge is that in the real world these beneficial microbes function in a whole (rhizosphere/phyllosphere) community (i.e., phytobiome), urging a shift toward studies that can shed light on how the effectiveness of these microbes in enhancing pest resistance is modulated in a community context (Lachaise et al, 2017). A fascinating emerging direction of research is the role of microbially produced and induced volatile organic compounds (VOCs) in plant-insect interactions (Rasmann et al, 2017), that can both deter herbivores (Sword et al, 2017) and attract their natural enemies (Coppola et al, 2017). They also play a crucial role in more complex plant-microbe-insect vector interactions.…”