Authors
M. L. Elliott and
E. A. Des Jardin, Fort Lauderdale Research and Education Center, University of Florida--IFAS, Davie 33314;
K. O'Donnell, Microbial Genomics Research Unit, Agricultural Research Service, United States Department of Agriculture, Peoria, IL 61604;
D. M. Geiser, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; and
N. A. Harrison and
T. K. Broschat, Fort Lauderdale Research and Education Center, University of Florida--IFAS, Davie
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. Within 2 to 3 months after onset of symptoms, the entire canopy becomes desiccated and necrotic but the leaves do not droop or hang down around the trunk. Based on pathogenicity and morphological and molecular characterization, the etiological agent has been identified as a new forma specialis of Fusarium oxysporum, designated f. sp. palmarum. Sequence analysis of a portion of the translation elongation factor 1-α gene (EF-1α) separated 27 representative isolates into two EF-1α groups, which differed by two transition mutations. Members of both EF-1α groups are pathogenic on both species of palm. A phylogenetic analysis inferred from partial EF-1α sequences from a genetically diverse set of F. oxysporum isolates, including three other formae speciales pathogenic on palm (i.e., f. sp. albedinis, f. sp. canariensis, and f. sp. elaeidis), suggested that f. sp. palmarum and f. sp. albedinis may be more closely related to one another than either is to the two other palm pathogens.
