AM fungal colonization minimizes disease damage on tomato during later life stages while delaying fruit development

Beneficial soil microbes, such as arbuscular mycorrhizal (AM) fungi, can help prepare plants for defense through a mechanism known as priming. Two of the most important unresolved questions in the field of AM fungal-mediated plant defense are (1) whether the effectiveness of priming remains consistent throughout the plant life cycle, and (2) whether the benefit of priming is context dependent. To address these questions, we initially fed Manduca sexta (tobacco hornworm) larvae on tomato (Solanum lycopersicum) plants that were treated with either live or sterile AM fungal inocula. We did this during the plants' first two stages: vegetative growth and flowering. We found no significant difference between the live and sterile AM fungal inocula treatments in terms of surface area eaten by the hornworms. This suggests that priming does not have any effect on herbivory defense in the early life stages of tomato. After flowering, an unexpected fungal pathogen arose among the plants that precluded the continued addition of hornworms. As a consequence, we carried out a second "experiment" during which disease progression, not herbivory, was monitored during the later life stages of tomato. For this second experiment, we found that plants given the live AM fungal inocula were significantly more resistant to the disease compared to plants given sterile inocula. This suggests that AM fungal colonization does provide tomato with a defensive benefit against disease during later life stages. However, fruit production was significantly delayed in plants given the live inocula, suggesting that the actual benefit of AM fungal colonization to plant fitness could depend on the timing and severity of the disease. Further research on AM fungal-mediated resistance to plant pathogens of varying severity and timing could help elucidate the context dependence of the benefits of AM fungi to plants.Center for Applied Plant Sciences OSU Undergraduate Research ScholarshipNo embargoAcademic Major: Evolution and Ecolog