A New Lethal Disease of Syagrus romanzoffiana and Washingtonia robusta in Florida is Caused by Fusarium oxysporum

Syagrus romanzoffiana and Washingtonia robusta are popular landscape ornamental palms grown throughout most of Florida. Since late 2004, we have noted mature specimens in the landscape and juvenile material in nurseries of S. romanzoffiana with symptoms not observed previously for this species. Symptoms are first observed on the oldest leaves, with individual leaves exhibiting chlorosis and necrosis initially only on one side. A distinct reddish-brown stripe is visible on the petiole and rachis, and there is a corresponding discoloration internally. Within 2-3 months after onset of initial symptoms, the entire canopy desiccates and turns brown as if freeze-dried in situ. Similar symptoms were observed on W. robusta beginning in the spring of 2007 in landscapes and a nursery. Fusarium oxysporum was consistently isolated from symptomatic petiole tissue from both palm species. DNA was extracted from single-spore isolates, and a portion of the translation elongation factor 1-alpha (TEF) was amplified using the polymerase chain reaction and the efl and ef2 primers. The resulting amplicons were sequenced. Comparison of the sequences obtained with TEF sequences in the FUSARIUM-ID database (http://fusarium.cbio.psu.edu) demonstrated that this F. oxysporum is likely to be a new forma speciales. Koch's postulates were completed using S. romanzoffiana and IV. robusta and F. oxysporum isolates obtained from both palm species. F. oxysporum isolates from S. romanzoffiana were pathogenic on W. robusta, and, likewise, isolates from IV. robusta were pathogenic on S. romanzoffiana.