Plants and animals are constantly in contact with microbes (microscopic organisms) that live on and inside them. This research will be an important first step in determining how competition between viruses is altered by the presence of beneficial bacteria and whether infection by viruses can reduce benefits from beneficial bacteria to their host plant, the common bean (Phaseolus vulgaris). This work benefits the public both directly by providing data that is relevant to agricultural crop production and indirectly through scientific education and outreach. Beans and other legumes are important, highly sustainable sources of dietary protein worldwide. A better understanding of microbial interactions in common beans can be used to inform strategies that could alter disease prevalence and increase crop yields. The pursuit of this knowledge will also provide a variety of hands-on research experiences for undergraduate students. Finally, the results of the research will be widely disseminated to the public through presentations to the community and the development of hands-on learning experiences and mini-courses for 6-12 grade students. The researchers will examine how the presence of additional mutualist microbial species in a host plant changes the outcome of virus competition and disease severity in coinfections and 2) whether infection by pathogens reduces the benefit that the host receives from mutualists. The ecological and evolutionary interactions between multiple pathogens which occupy the same host will be studied, using a system of viruses infecting the common bean. Mutualists have the potential to alter competitive outcomes between coinfecting pathogens by influencing host resources for growth and defense. At the same time, pathogens can induce a full immune response by the host that can be damaging to microbial mutualists. If pathogen infection reduces the benefit that the host receives from mutualists, this might destabilize the association. Common beans infected with pathogenic viruses and mutualistic nitrogen-fixing bacteria (rhizobia) offer a highly tractable system for studying the interactions between coinfecting pathogens and mutualists. Two measures of pathogen competitive ability, within host concentration and transmission between hosts, will be compared in plants with and without rhizobia to evaluate whether the presence of a mutualist is differentially beneficial to one pathogen species. The impact of pathogen infection on the viability of the mutualism will be quantified by measuring plant immune response hormones as well as rhizobial root colonization and nitrogen fixation.
