|Van Berkum, Peter|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2003
Publication Date: 9/26/2003
Citation: Bao, J., Fravel, D. R., Lazarovits, G., Chellemi, D., van Berkum, P., and O¿Neill, N. 2004. Biocontrol genotypes of Fusarium oxysporum from tomato fields in Florida. Phytoparasitica 32:9-20. Interpretive Summary: Methyl bromide is being phased out due to its role in ozone destruction. Fusarium wilt of tomato, caused by the fungus Fusarium oxysporum, is currently controlled by soil fumigation with methyl bromide. Some nonpathogenic, biocontrol strains of F. oxysporum can reduce losses to Fusarium wilt. The pathogenic and nonpathogenic strains look the same. This research was undertaken to understand the genetic relationships among pathogenic, biocontrol and other Fusarium species, as well as to find genetic markers to distinguish among the groups. Fusarium was isolated from soil and roots that were collected from an organic and a conventional farm in Florida. The isolates were tested for pathogenicity and biocontrol ability. DNA was extracted and portions of it were sequenced or analyzed by random amplified polymorphic DNA (RAPD). The biocontrol strains were related to the pathogens, but showed independent evolutionary origins. RAPD patterns could not distinguish biocontrol strains from pathogenic or other Fusarium oxysporum strains. These results will be used by scientists developing alternative control methods for Fusarium wilt.
Technical Abstract: The diversity of Fusarium oxysporum isolated from two Florida tomato fields (organic and conventional farms) was studied to explore the relationships among pathogenic, saprophytic and biocontrol Fusarium spp. More than 63,000 fungal colonies were recovered, including 21,826 Fusarium spp., with 3110 of these tentatively identified as F. oxysporum. From 5.3 to 13.5% of the fusarium recovered from samples from the organic farm were F. oxysporum and from 36.4 to 49.8 % of the fusarium recovered from the conventional farm was F. oxysporum. Eleven different species of Fusarium were recovered from the organic farm and eight from the conventional farm. Sixty-six (21.9%) of 302 F. oxysporum isolates were pathogenic to tomato, including 31 and 35 isolates identified as F. o. lycopersici with three races and F. o. radicis-lycopersici, respectively. In greenhouse bioassays which included the known biocontrol agents F. oxysporum strains CS-20 and Fo47, nonpathogenic strains (305, 81, and 16 isolates of F. oxysporum, F. proliferatum, and Fusarium sp., respectively) revealed a range of biocontrol ability in a normal distribution.