Domestication, Fertilization, and Nodulation: Assessing the Role of Anthropogenic Impositions on the Symbiosis between Phaseolus vulgaris L. and Nitrogen-fixing Bacteria
Open Access
Author:
Fry, Gwendolyn
Area of Honors:
Anthropology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Liana T Burghardt, Thesis Supervisor Laurel Nichole Pearson, Thesis Honors Advisor George H Perry, Faculty Reader
Phaseolus vulgaris L. (Latin American common bean) is a leguminous crop that is significant in the life histories of both human civilization and nitrogen-fixing bacteria called rhizobia. These associations are evident from the impacts they have left on the genome of the common bean. As a legume, the common bean has several genes that code for the initiation and maintenance of mutualistic endosymbiosis with rhizobia. Over the course of its domestication and cultivation, the common bean has also undergone simultaneous artificial selection and multiple bottlenecks. As it exists in commercial agriculture, crops of common bean lack within-population genetic diversity and are widely considered poor at facilitating nitrogen fixation. Recent studies suggest nitrogen fertilization to be key in the decline of nodulation in cultivars of common bean. In addition, preliminary research suggests that wild lineages of bean have greater numbers of nodules. However, these data do not directly compare proxies of nitrogen fixation, like nodulation, with genotype and the presence of nitrogen fertilizer. I hypothesized that bean accession would be a more significant factor than nitrogen presence in determining the ability to facilitate nitrogen fixation. Through a randomized block greenhouse experiment that observed the variables of accession and nitrogen treatment, I found that both nitrogen fertilization and genotype were significant contributors to root:shoot ratio, nodule number, and chlorophyll content index (CCI) in common bean. However, bean genotype was more significant in determining ability to facilitate nitrogen fixation.