|Des jardin, E|
Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/7/2009
Publication Date: 2/28/2010
Citation: Elliott, M.L., Des Jardin, E.A., O Donnell, K., Geiser, D.M., Harrison, N.A., Broschat, T.K. 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. Interpretive Summary: The focus of this study was to characterize the pathogen or pathogens responsible for the rapid death of two species of palms used extensively in landscapes in the southern half of Florida. A new disease of queen palm (Syagrus romanzoffiana) and Mexican fan palm (Washingtonia robusta) has spread across the southern half of Florida during the past 5 years. Symptoms, which suggest the disease is new, include death of the palms within 2 to 3 months after onset of initial symptoms and extreme drying of the leaves that remain in place. Results of pathogenicity and DNA typing experiments indicate the disease of both palms is caused by the same fungal pathogen, which we have designated as a new host-specific form, Fusarium oxysporum f. sp. palmarum. This novel palm pathogen is closely related to but distinct from the date palm pathogen, F. oxysporum f. sp. albedinis, suggesting that they may share a common evolutionary origin. Knowledge gained from the characterization of the novel palm pathogen will help plant disease specialists monitor and prevent the further spread of this disease in Florida and it will assist plant breeders develop cultivars with broad-based resistance to the pathogen.
Technical Abstract: A new disease of Syagrus romanzoffiana (queen palm) and Washingtonia robusta (Mexican fan palm) has spread across the southern half of Florida during the past 5 years. The initial foliar symptom is a one-sided chlorosis or necrosis of older leaf blades, with a distinct reddish-brown stripe along the petiole and rachis and an associated discoloration of internal tissue. This disease kills its palm hosts within 2 to 3 months after onset of initial symptoms, resulting in a desiccated and necrotic canopy that appears freeze-dried in situ. Based on pathogenicity and molecular characterization, the etiological agent has been identified as a new forma specialis of Fusarium oxysporum designated f. sp. palmarum. Sequencing of a portion of the translation elongation factor 1-alpha gene (EF-1alpha) separated 27 representative isolates into two EF-1alpha groups, which differed by two transition mutations. Members of both EF-1alpha groups are pathogenic on both species of palms. A phylogenetic analysis inferred from partial EF-1alpha sequences from a genetically diverse set of F. oxysporum isolates, including three other formae speciales pathogenic on palms (i.e., f. sp. albedinis, f. sp. canariensis, and f. sp. elaeidis), suggested that f. sp. palmarum and f. sp. albedinis may share a recent common ancestor.