Seventy-four Fusarium oxysporum soil isolates were assayed for known effector 
genes present in an F. oxysporum f. sp. lycopersici race 3 tomato wilt strain 
(FOL MN-25) obtained from the same fields in Manatee County, Florida. Based on 
the presence or absence of these genes, four haplotypes were defined, two of 
which represented 96% of the surveyed isolates. These two most common effector 
haplotypes contained either all or none of the assayed race 3 effector genes. We 
hypothesized that soil isolates with all surveyed effector genes, similar to FOL 
MN-25, would be pathogenic toward tomato, whereas isolates lacking all effectors 
would be nonpathogenic. However, inoculation experiments revealed that presence 
of the effector genes alone was not sufficient to ensure pathogenicity on 
tomato. Interestingly, a nonpathogenic isolate containing the full suite of 
unmutated effector genes (FOS 4-4) appears to have undergone a chromosomal 
rearrangement yet remains vegetatively compatible with FOL MN-25. These 
observations confirm the highly dynamic nature of the F. oxysporum genome and 
support the conclusion that pathogenesis among free-living populations of F. 
oxysporum is a complex process. Therefore, the presence of effector genes alone 
may not be an accurate predictor of pathogenicity among soil isolates of F. 
oxysporum.