PhD defence by Guadalupe Z. Hernandez
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Title of thesis: Resistance-inducing benefits from root-associated entomopathogenic fungi in the context of biological interaction with arbuscular mycorrhizal fungi Many fungi live intimately associated with plants and may benefit or harm the host plant. Soil microorganisms such as the arbuscular mycorrhizal fungi (AMF) and the entomopathogenic fungi (EPF) have shown beneficial effects on plant health. While the AMF has an obligate symbiosis with plants, the EPF are mainly insect pathogens. So far, most studies have evaluated the effect of individual microbial inoculants on plant defense. Therefore, this PhD work focused on the evaluation of the induction of plant defense and growth when EPF and AMF were root-inoculated individually and in combination. First, a screening of nine EPF isolates was performed by evaluating plant growth and protection against the aboveground insect herbivore Spodoptera exigua. Second, three EPF isolates of B. bassiana, M. brunneum and M. robertsii were combined with the AMF Funneliformis mosseae to evaluate the effects on plant defense against the foliar phytopathogen Botrytis cinerea. Later, the AMF Rhizophagus irregularis was combined with the same EPF isolates to test the effects on tomato plant defense against S. exigua and to evaluate the production of the specialized metabolites α-tomatine and dehydrotomatine and the induction of defense genes. Finally, the effects of the EPF B. bassiana and M. robertsii, the AMF R. irregularis and their combinations were evaluated on plant defense and growth under realistic tomato production conditions. The results showed that the EPF played a role in the protection in tomato plants against a phytopathogen under greenhouse conditions and against the natural incidence of insect pests under field conditions. Nevertheless, this effect was isolate dependent. The beneficial effect of AMF whether alone or in combination with EPF was on plant growth. Even though the combination of EPF and AMF did not enhance plant defenses, these groups of fungi have complementary functional roles. However, the results varied between the experimental repetitions for all the trials performed, suggesting a high context-dependency of plant-microbe interactions. Such variable results may comprise a constraint for the future uptake and use of beneficial fungi in plant production.
There will be a reception at SOBI after the defense
Supervisor: Assessment committee: Section secretary: Organizer: |