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Abstract

Members of the genus听厂迟谤别辫迟辞尘测肠别蝉听are some of the best candidates for biological control of soil-borne pathogenic bacteria. Antibiotic production by听厂迟谤别辫迟辞尘测肠别蝉听is thought to be crucial for this strain鈥檚 ability to compete with other closely related soil microorganisms. Furthermore,听厂迟谤别辫迟辞尘测肠别蝉听is able to not only inhibit the growth of its competitors, but also that of many soil-borne plant pathogens. My thesis assessedStreptomyces听performance under varying levels of soil resources (carbon componds that serve as energy sources) and in plots with varying degrees of plant diversity that, in turn, affects soil resources. This project aims to deconvolute the confounding effects of these environmental variables on plant pathogen suppression by听Streptomyces. I characterized soils from low-diversity plant communities (monoculture) and high-diversity plant communities (polyculture (16-species)), while providing fungicide treatment to the leaves of the plant, which has been found to increase plant productivity, to half of the plots. I found that听厂迟谤别辫迟辞尘测肠别蝉听associated with听plant monoculture versus plant polyculture is more likely to be subject to resource competition. In contrast,厂迟谤别辫迟辞尘测肠别蝉听communities in polyculture are much more complex than those associated with plant monoculture. Therefore, in monoculture agricultural system,听Streptomycesstrains听are likely to help suppress plant disease via antibiotics production, and attempts to control soil-borne plant diseases via antibiotics-producing听Streptomyces听strains should work well in plant monoculture (but perhaps not in plant polyculture). My findings also suggest that the inhibitory phenotypes of听Streptomyces听(that differ genetically from non-inhibitory strains, as indicated by our 16S sequencing data) are induced by low soil carbon quantity. Finally,听厂迟谤别辫迟辞尘测肠别蝉听responds to low plant diversity and low carbon levels in the soil by not only producing more antibiotics but also increasing their own resistance to antibiotics.