Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Abstract Only
Publication Acceptance Date: September 19, 2000
Publication Date: N/A
Fusarium wilt in tomatoes is currently controlled by soil fumigation with methyl bromide prior to planting. This chemical will be banned in 2005. This research was undertaken to determine the population structure of Fusaria and to identify genetic markers for pathogenicity and biocontrol ability. Roots and soil were collected from tomato plants at conventional and organic farms in Osceola County, FL. A total of 21,054 Fusaria were recovered, 26.6% of which were F. oxysporum. Rhizosphere soil had 10-fold larger Fusarium population sizes than non-rhizosphere soil. Fine roots had population sizes 2 to 7 fold greater than larger roots. Soil treated with Telone had the largest fungal population of any site tested. Of the 406 F. oxysporum recovered, 63 were pathogenic (34 F. o. lycopersici; 29 F. o. radicis-lycopersici). All of the 34 pathogenic F. o. lycopersici were from the organic farm. Of these,15 were Race 1, 6 were Race 2 and 5 were Race 3. However, when samples were originally collected, no plants on the organic site showed symptoms, while several plants at the conventional site showed symptoms and race 3 F. o. lycopersici was recovered from these plants. Isolates were characterized using ITS1-5.8S-ITS2 rDNA regions. The ITS1-5.8S-ITS2 region was amplified using ITS4 and ITS5 primers, digested using MspI, and then separated on an agarose gel. At least 5 groups were identified based on polymorphism of the ITS1-5.8S-ITS2 rDNA regions. Group II (one MspI cut site) had 82 isolates, including nearly all the pathogenic strains. Group III (2 cuts) had 17 isolates; and Group V (3 cuts) had 4 isolates. There was greater diversity in the nonpathogenic than in the pathogen populations.