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Title: Genetic Variability Among Isolates of Fusarium oxysporum from Sugar Beet

Author
item Hill, Amy
item Reeves, Patrick
item Larson, Rebecca
item Fenwick, Ann
item Hanson, Linda
item Panella, Leonard

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2010
Publication Date: 1/1/2011
Citation: Hill, A.L., Reeves, P.A., Larson, R.L., Fenwick, A.L., Hanson, L.E., Panella, L.W. 2011. Genetic Variability Among Isolates of Fusarium oxysporum from Sugar Beet. Journal of Plant Pathology. 60(3): 496-505. DOI:10.1111/j.1365-3059.2010.02394.x.

Interpretive Summary: Fusarium Yellows is a disease of sugar beet that is caused by a common soil fungus, FOB (Fusarium oxysporum f. sp. betae). This disease is a problem in the United States and Europe and causes reduction in root yield, juice purity, and the amount of sucrose produced in affected sugar beet. Fusarium yellows causes both leaf (wilting, yellowing, leaf death) and root (a gray to brown internal discoloration) symptoms. FOB is quite variable in it appearance when grown in the lab, the amount of disease that it causes, its symptoms, and the types of plants that it can attack. Isolates of this fungus from sugar beet, dry bean, and spinach, as well as other types (species) of this fungus were collected from diseased plants. In greenhouse tests, all those collected were tested for their ability to cause disease on sugar beet (pathogenicity). We chose a group of these fungi collected from sugar beet from different geographical areas, both those that caused disease and those that didn’t. We used their DNA to see how closely they were related. There were no closely related groups that consisted exclusively of FOB types or types from a single geographic origin. We conclude that these fungi from sugar beet more than likely have more than one distinct lineage.

Technical Abstract: Fusarium Yellows, caused by the fungus Fusarium oxysporum f. sp. betae (FOB), can lead to significant yield losses for sugar beet growers. This fungus is variable in pathogenicity, morphology, host range, and symptoms; and, it is not a well characterized pathogen on sugar beet. From 1998 – 2003, 86 isolates of F. oxysporum from sugar beet, twenty other Fusarium species from sugar beet, four F. oxysporum isolates from dry bean, and five F. oxysporum isolates from spinach were obtained from diseased plants and characterized by pathogenicity. A group of Fusarium isolates from different geographical areas, including nonpathogenic and pathogenic F. oxysporum, F. solani, F. proliferatum, and F. avenaceum from sugar beet, F. oxysporum from dry bean and spinach, and Fusarium DNA from Europe were chosen for phylogenetic analysis. Sequence data from ß- tubulin, EF1a, and ITS, were used to examine whether Fusarium diversity was tied to geographic origin and pathogenicity. Parsimony bootstrap and Bayesian MCMC analysis of individual and combined datasets revealed three unique clades, pathogens from Oregon, F. solani, and F. proliferatum, and two small groups of nonpathogens. However, finding FOB isolates in clades predominately made up of other Fusarium species suggests that F. oxysporum from sugar beet is most likely not monophyletic.