|Pettway, Rodney - UNIVERSITY OF MINNESOTA|
|Katan, T - VOLCANI CENTER, ISRAEL|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2001
Publication Date: N/A
Interpretive Summary: A disease of tomato known as "crown rot" was first reported in the mid 1970's from widely separated geographic locations including Japan, Canada, California, Ohio and Florida. Since that time, the disease has spread to other tomato growing nations in Europe and the Middle East. Recently, we have used DNA fingerprinting to trace the origin of the crown rot pathogen found in Europe. Surprisingly, the predominant strain of this fungal pathogen recently isolated in England, the Netherlands and Belgium was very closely related to a strain of the pathogen found in Florida. Further genetic analysis of over 300 strains of the fungus from Florida indicates that the origin of the European epidemic was due to transportation of the pathogen in the last 10 years from Florida, most likely Palm Beach county, to the Netherlands. Application of quarantine restrictions for plant pathogenic fungi requires scientific documentation of the risks of long distance movement of the pathogens. Such movement is very difficult to prove without clearly defined genetic markers to document the link between the source pathogen population and the appearance of the pathogen in another part of the world. This research establishes the foundation upon which movement of this tomato pathogen can be measured. The approach used in this research can be applied to a wide range of fungal pathogens of other crops as well.
Technical Abstract: Fusarium oxysporum samples from tomato plants displaying crown and root rot symptoms were collected in central and southern Florida and analyzed using vegetative compatibility grouping (VCG) and nuclear RFLP data. VCG 0094, previously known only from northwestern Europe, was predominant among 389 isolates assessed. Two additional, newly described VCGs of the crown rot pathogen (0098 and 0099) were detected at low frequencies. Detailed analysis of vegetative compatibilities revealed three distinct subgroups among the European VCG 0094 isolates, whereas the Florida VCG 0094 isolates displayed a continuum of compatibilities. RFLP haplotypes were constructed using one repetitive and three low-copy probes. Population subdivision of VCG 0094 collected from various Florida counties and northwest Europe (Netherlands, Belgium, United Kingdom) was evaluated by analysis of molecular variance(AMOVA). We revealed a "natural" population structure that separated the Florida Eastcoast from the West coast population. In addition, isolates from Europe were statistically indistinguishable from the population from Palm Beach County, Florida. Furthermore, gene diversity among Palm Beach VCG 0094 isolates was more than five times greater than among European isolates. Results from both VCG and RFLP analysis strongly support the inference that the European VCG 0094 constitutes a founder population, which resulted from inter-continental migration of a few isolates from Florida, and more specifically Palm Beach County.