The Mycorrhizal Status of Potatoes Alters Plant Physiology and the Fitness of a Chewing Insect Pest

Arbuscular mycorrhizal fungi (AMF) naturally occur in soils and are known to form symbiotic relationships with plant roots, mainly aiding in the acquisition of nutrients such as phosphate. In addition, some mycorrhizal plants may exhibit enhanced shoot growth and tolerance to biotic stresses such as insect herbivory. This research involves potato (Solanum tuberosum), the cabbage looper (Trichoplusia ni) a generalist leaf-chewing insect in its larval stage, and the generalist AM fungus Glomus intraradices. The goal of this research was to investigate the potential underlying mechanism involved in mycorrhiza-induced resistance against cabbage loopers. The impact of this tripartite interaction was evaluated by: (a) comparing biomass accumulation of cabbage looper larvae both before and after feeding on mycorrhizal/non-mycorrhizal potato plants, (b) assessing plant physiology status, and (c) measuring plant gene expression. Our results showed that cabbage looper larvae accumulated less biomass after 8 days of feeding on mycorrhizal plants compared to non-mycorrhizal plants. Given the duration of this study, mycorrhizal plants only exhibited minor changes in plant physiology, including increased dry shoot weight. Interestingly, transcript levels of insect-induced defense genes significantly increased in mycorrhizal plants that were damaged by cabbage loopers compared to damaged non-mycorrhizal plants providing evidence for mycorrhiza-induced resistance.