How Many Hosts Can Fusarium oxysporum ff. spp. canariensis and palmarum Affect?

Formae speciales of the fungus Fusarium oxysporum are defined based on pathogenicity to one or more plant hosts.  Both Fusarium oxysporum ff. spp. canariensis (Foc) and palmarum (Fop) cause Fusarium wilt of palms in Florida, with Foc’s primary host being Phoenix canariensis and Fop’s primary hosts being Syagrus romanzoffiana and Washingtonia robusta.  Over the past 5 years, both pathogens have been isolated from other palm hosts.  Pathogenicity studies have been initiated using palm seedlings to examine the host range for each pathogen. The primary problem initially encountered in these experiments was obtaining consistent results with the Phoenix species.  It was determined that for both Foc and Fop, the most consistent results are obtained when the bottom 5 cm of the root system is cut off prior to inoculation. Preliminary data indicates that Foc can also affect P. sylvestris and P. reclinata but not S. romanzoffiana and W. robusta, while Fop can also affect W. filifera, P. canariensis, P. dactylifera, P. reclinata, P. sylvestris and the hybrid S. romanzoffiana x Butia capitata.  It was observed that both W. robusta and W. filifera are highly susceptible to Fop, with both palm species usually dying within 4 weeks of inoculation, even when the root system is left intact.