Biocontrol genotypes of Fusarium oxysporum from tomato fields in Florida

The diversity of Fusarium oxysporum isolated from two Florida (USA) 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. Of the Fusarium recovered from samples, in the organic farm 5.3-13.5% and in the conventional farm 36.4-49.8% were E oxysporum. Eleven different species of Fusarium were recovered from the organic farm and eight from the conventional farm. Sixty-six (21.9%) of 302 E 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 that 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. Random amplified polymorphic DNA (RAPD) analysis indicated that 15 out of 20 high biocontrol ability E oxysporum isolates were clustered closely, but they did not have a unique RAPD pattern to differentiate them from saprophytic or pathogenic isolates.