Abstract:
The use of endophytic fungi has dramatically increased plant performance through the
enhancement of plant protection against abiotic and biotic stressors. We previously
demonstrated that the endophytic fungus Trichoderma asperellum M2RT4 improves
tomato defenses against the tomato leafminer Tuta absoluta through the reduction
of oviposition, leafmining, pupation, and adult emergence. However, the underlying
mechanism by which the presence of this endophytic fungus within tomato host
plant affects T. absoluta host selection and life-history traits is unknown. We tested
the behavioral responses of T. absoluta in Y-tube olfactometer bioassays and found
that females preferred non-inoculated tomato plants against those inoculated by
endophytes. Additionally, T. absoluta females were not attracted to non-inoculated
infested nor to inoculated-infested tomato plants. Chemical analysis revealed the
emission of methyl salicylate in inoculated tomato plant and an increase in the amounts
of monoterpenes emitted from non-inoculated infested plants. Additionally, we found
that upon herbivory, T. asperellum M2RT4 modulates tomato plant chemistry through
the production of (Z)-jasmone thus activating both salicylic and jasmonic acid defense
pathways. Further, T. absoluta females were attracted to monoterpernes including
α-pinene, 2-carene, and β-phellandrene but repelled by methyl salicylate. Methyl
salicylate could therefore be considered as a good semiochemical-based candidate
for sustainable T. absoluta management using a “push-pull” approach. However, in
dose-response bioassays, females of T. absoluta did not show any preference to
the four component-blend (α-pinene, 2-carene, β-phellandrene, and methyl salicylate).
(Z)-jasmone-treated tomato leaflets significantly reduced the leafmining activity of
the pest at the concentration of 10 ng/µL and causing the highest larval mortality
rate (83%) with the shortest LT50 (1.73 days) 7 days post-treatment. T. asperellum
M2RT4 effect on herbivore performance was then (Z)-jasmone-mediated. These findings expand our understanding of how the endophytic fungus T. asperellum
M2RT4 could mediate chemical interactions between T. absoluta and its host plant
which are potentially important for development of environmentally friendly T. absoluta
management programs.
