Fusarium oxysporum f.sp. palmarum: a new disease of ornamental palm trees
Since 2004, a new lethal disease of two ornamental palm species, Syagrus romanzoffiana (queen palm) and Washingtonia robusta (Mexican fan palm), has been observed in the South of Florida (US). S. romanzoffiana and W. robusta are widely planted in Florida landscapes because they are relatively cold tolerant and resistant to Coconut lethal yellowing phytoplasma (EPPO A1 List). On affected S. romanzoffiana and W. robusta, the initial foliar symptom is a one-sided chlorosis or necrosis of older palms, with a distinct reddish brown stripe along the petiole and rachis, associated with a discoloration of internal tissues. The entire canopy then becomes dessicated and necrotic but does not collapse. Palm trees are rapidly killed within 2 to 3 months of the onset of symptoms (pictures can be viewed on the Internet, see link below). Studies (morphology, molecular characteristics, pathogenicity) showed that the causal agent is a new forma specialis of Fusarium oxysporum which has been designated as Fusarium oxysporum f.sp. palmarum. Comparison with other Fusarium wilt disease agents (i.e. F. oxysporum f.sp. albedinis (EPPO A2 List), F. oxysporum f.sp. canariensis, F. oxysporum f.sp. elaeidis) showed that its closest relative was F. oxysporum f.sp. canariensis. In these studies, most samples were obtained from palm trees that had been planted in the landscape for 5 to 20 years. However, some juvenile palm trees showing disease symptoms have also been found in three nurseries (1 container nursery and 2 field nurseries), but as affected plants quickly died they could not be marketed. It is not known how the disease spreads in the landscape, but it is suspected that wind-blown spores could play a major role and that contaminated pruning tools could also transmit the pathogen from one tree to another. More studies are needed to better understand the epidemiology of the disease and to determine possible control measures.
Elliott ML, Des Jardin EA, O’Donnell K, Geiser DM, Harrison NA, Broschat TK (2010) Fusarium oxysporum f.sp. palmarum, a novel forma specialis causing a lethal disease of Syagrus romanzoffiana and Washingtonia robusta in Florida. Plant Disease 94(1), 31-38.
Internet (last accessed 2010-11)
University of Florida. Fusarium wilt of queen palm and Mexican fan palm by ML Elliott (dated June 2010). http://edis.ifas.ufl.edu/pdffiles/PP/PP27800.pdf