Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/1995
Publication Date: N/A
Interpretive Summary: The roots of healthy cotton plants taken from cotton field soil and assayed for the presence of fungi proved to be extensively colonized by Fusarium species. Many of these isolates proved to be harmless to cotton roots and thus have potential as biocontrol agents. Only a few isolates of Fusarium solani and Fusarium oxysporum proved harmful to cotton under ideal conditions, and these were not harmful under less than optimum conditions. Several Fusarium isolates produced chemicals in culture that were harmful to cotton, and their effects could be mistaken for disease caused by the fungus. However, when the chemicals were removed the fungus caused no symptoms of disease on the cotton plants. One isolate, Fusarium nygamai proved to be a new species record for the United States.
Technical Abstract: Healthy appearing cotton seedling roots (symptomless) grown in soil (Lufkin fine sandy loam) collected from a cotton field were extensively colonized by Fusarium species. The species recovered included F. oxysporum, F. solani, F. equiseti, F. nygamai, F. semitectum and F. moniliforme. Fusarium oxysporum and F. solani were the dominant species. Fusarium nygamai, which was frequently found, proved to be a new species record for the United States. Pathogenicity tests of 97 Fusarium isolates showed that 11 F. solani and 3 F. oxysporum isolates were pathogenic to cotton, and that Fusarium equiseti, F. nygamai and F. semitectum isolates were not pathogenic. Pathogenic isolates reduced seedling growth and caused necrotic lesions on the taproots and secondary roots. Pathogenic isolates of Fusarium solani were more virulent to cotton seedlings than those of F. oxysporum. Apparently, pathogenic Fusarium isolates are present on apparently healthy seedling roots, but do not incite disease under nonconducive environmental conditions. Fusarium nygamai produced phytotoxins in culture media, and symptoms produced by the phytotoxins could be mistaken for pathogenesis. This suggests that caution must be taken in inoculum preparation, and in drawing conclusions about the pathogenicity of Fusarium species to cotton plants.