|Van Berkum, Peter|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2002
Publication Date: N/A
Citation: N/A Interpretive Summary: The soil fumigant methyl bromide is being phased out due to its destruction of ozone. We are developing biocontrol as an alternative to methyl bromide for control of Fusarium wilt on tomato. Our best biocontrol agents are also Fusaria. Currently, we cannot distinguish pathogenic Fusaria from beneficial ones, or from saprophytic Fusaria (neither pathogenic nor beneficial) without seeing how plants react to them. This research was undertaken to study the genetic diversity in Fusarium populations and to discover genetic markers for pathogenicity and biocontrol ability. Three methods [vegetative compatibility group(VCG); sequencing ribosomal DNA (rDNA)in two regions(ITS1 and ITS2) and the 5.8S rRNA gene; amplified fragment length polymorphism (AFLP)]were used to analyze 41 F. oxysporum strains and one F. solani strain from tomato roots worldwide. All methods showed that pathogen populations were less diverse than the nonpathogens, suggesting that pathogens arose from a common ancestor and nonpathogens arose locally. While pathogens could be distinguished from other Fusaria by genetic markers, beneficial Fusaria could not be distinguished from saprophytic ones. These results will be used by scientists developing control strategies for Fusarium wilt.
Technical Abstract: Forty-one Fusarium oxysporum strains and 1 F. solani strain, mostly from tomato roots worldwide, were used to analyze population diversity using vegetative compatibility group (VCG), sequencing of ribosomal DNA (rDNA)internal transcribed spacers (ITS1; ITS2) and the 5.8S rRNA gene, and amplified fragment length polymorphism (AFLP). Eighteen F. oxysporum strains were nonpathogenic to tomato and 21 pathogenic (14 F.o. lycopersici; 7 F.o. radicis-lycopersici). Most F.o. lycopersici strains were VCG 0030,while most nonpathogenic strains were incompatible with tester strains. ITS sequences indicated four clusters, with nonpathogens in Groups I and II, and pathogens in Groups III and IV. AFLP also showed that pathogens and nonpathogens were in 4 separate clusters,but some pathogens were with nonpathogens. Results of all 3 methods showed that the pathogen population was less diverse than the nonpathogen population, suggesting that tomato pathogenic strains were likely monophyletic in origin. For all strains, there was no relationship between genetics and geographic origin, suggesting that local origin of pathogen was unlikely. Data were not sufficient to distinguish biocontrol strains from saprophytic F. oxysporum strains.