Interazioni multi-livello tra piante e altri organismi: valutazione dell'effetto delle carenze nutrizionali e dei composti volatili prodotti dai microorganismi del suolo sulle risposte difensive della pianta nei confronti delle larve di Spodoptera spp.

Nowadays, yield losses due to insect pests is one of the biggest issues for agricultural production. Since the request for food supply is growing and the use of pesticides can be harmful for human health and for other beneficial organisms, the demand for new agricultural management practices and for more environmental-friendly technologies is increasing. Indeed, a growing number of studies focuses on the manipulation of environmental factors affecting plant health and productivity, in order to grow resistant crop species in a more sustainable way. The overall aim of the thesis was to evaluate the effect of both abiotic and biotic factors on plant responses to generalist insect pests, like Spodoptera spp. larvae. In particular, two specific objectives were considered: 1) investigating the effect of iron (Fe) deficiency on plant (Lima bean (Phaseolus lunatus) and cucumber (Cucumis sativus L.)) defence responses to Spodoptera larvae; 2) investigating the effect of plant-bacteria interaction belowground on plant (Solanum lycopersicum) defence responses to Spodoptera spp. larvae (this activity was performed at NIOO-KNAW Research Institute of Wageningen (NL)). The effect of Fe deficiency on plant responses to pest attacks was evaluated in terms of changes in leaf nutrient content, membrane potential values (Vm) and volatile compound (VOCs) production. Whereas, the activity related to the second objective was performed by testing the role of a rhizobacteria consortium (Bacillus drentensis, Burkholderia strain AD24 and Paenibacillus strain AD87) in the induction of plant resistance (ISR) both through VOCs-mediated interaction from distance (pot-in-jar system in the greenhouse) and direct inoculation (in vitro). Plant-induced resistance was evaluated in terms of leaf glandular trichome (type VI) production and pest performance. Preliminary results suggest that, depending on the plant species and on the severity of Fe deficiency, such nutritional disorder affects i) leaf nutrient content and distribution over the plasma membrane impairing physiological depolarization of membrane potential after herbivory and ii) pest performance by undermining leaf nitrogen content as well as by increasing GLVs emission. Concerning plant-bacteria interaction, it is possible to assert that VOCs-mediated interaction affected plant responses to insect pests: significant difference between plants exposed to volatiles and control plants, in terms of weight gained by larvae after leaf feeding, was detected, even though contrasting results were observed depending on the type of pest performance assay that was used. Moreover, soil resident microbial communities, rather than seed biopriming, demonstrated strong influence on plant growth and trichome production in the greenhouse experiment. Although nutrient and VOCs analyses are still in progress and further studies are needed, this work highlighted the importance of investigating plant acclimation process in response to stressful conditions, considering multi-level interactions among abiotic and biotic factors that occur in the environment.