Whose Phenotype is it Anyway? The Complex Role of Mycorrhizal Fungi in the Expression of Plant Defense

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Plants worldwide must defend themselves from being damaged by their enemies, including insects, deer and pathogens. Plant defenses range from physical defenses, like thorns, spines, and tough leaves, to chemical defenses such as cyanide and steroids. As plants try to defend themselves, most of them make use of nutrients that are provided to them by fungi (called mycorrhizae) that live in their roots. In what is basically a barter system, plants provide the fungi with sugar while the fungi provide plants with minerals such as phosphorus. The strength of plant defenses may vary with the amount of fungus in their roots and the identity of their fungal partners, but this has never been studied in detail.Using common milkweed as a study plant, this research explores how the strength of plant defense varies with the fungal colonization of roots. It examines how variation in plant and fungal identity contributes to defense, and how natural variation in soil nutrients influences the barter system. Experiments also explore the effects of root fungi on insect herbivores. The results of this work will contribute to an understanding of how diverse plant species, from agricultural crops through forest trees, use root fungi in their defense strategies. It may be possible to manipulate root fungi to protect the plants that are important to humans or to render defenseless those that are invasive pests. The research will also help to train the next generation of biologists both in universities and in local area schools.