Dissertation Research: Effects of legume-rhizobia symbiosis on plant-insect interactions

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The coevolved mutualism between legumes and nitrogen fixing rhizobia bacteria is distinguished by its capacity to increase soil fertility. While many aspects of the legume-rhizobia interaction have been well-characterized, little is known about the effects of this mutualism on other organisms, particularly herbivores. Physiological changes induced in legume plants upon inoculation with rhizobia may alter plant defenses and nutritional quality of the host. Moreover, the nature and intensity of such effects may vary across rhizobial strains, which may thus confer different levels of resistance to host plants. The objectives of this project are to: 1) characterize the effects of rhizobia on the performance of herbivores from different feeding niches; 2) determine how plant responses to herbivory are altered by inoculation; and 3) distinguish rhizobia strain-specific effects on plant resistance to herbivores. Experiments will be performed on soybean plants receiving nitrogen from rhizobia, nitrate fertilizers, or a combination of the two. This study will provide new insights into the role of herbivores in the evolution of the legume-rhizobia mutualism. Exploring mechanisms by which rhizobia may protect host plants from herbivores may facilitate the development of novel and more efficient inoculants for crop plants and thus contribute to sustainable agricultural practices.