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Laurel wilt disease: An exceptional Black Swan event.
J. A. SMITH (1), R. C. Ploetz (2), J. Hulcr (1), J. McCutcheon (3), T. J. Dreaden (1), M. A. Hughes (1), D. Spence (4), K. Shin (1), S. Inch (5), J. Ploetz (2), A. Campbell (6). (1) School of Forest Resources and Conservation, University of Florida, Gainesville, FL, U.S.A.; (2) Tropical Research and Education Center, University of Florida, Homestead, FL, U.S.A.; (3) University of Montana, MIssoula, MT, U.S.A.; (4) Florida Native

Ambrosia beetles normally attack weak or dying trees where they cultivate and feed on their typically non-pathogenic fungal symbionts. Native and cultivated trees in the Lauraceae in the southeastern US are being devastated by laurel wilt (LW), caused by the exotic fungal pathogen, <i>Raffaelea lauricola</i> which is transmitted to trees by the Asian redbay ambrosia beetle (<i>Xyleborus glabratus</i>). In little more than a decade, LW has killed hundreds of millions of redbay trees and threatens the avocado industries in Florida (valued at > $60 million/year) and California ($400 million). The pathogen is unique since it is highly virulent to host trees, with as few as 100 conidia being sufficient to induce disease. Microscopic observations and studies with secondary metabolites indicate that hosts over-react to the presence of the pathogen leading to vascular dysfunction, but toxins are likely not involved in pathogenesis. Genetic analyses of <i>R. lauricola</i> indicate that a single clone occurs in the USA and comparisons of microsattelite loci of the pathogen in the USA indicate a close match with isolates in Taiwan. Lateral transfer of the pathogen to other ambrosia beetle species has been observed in Florida. Strategies to manage LW focus on use of systemic fungicides, early detection and sanitation in avocado orchards and host resistance. Genomic analyses <i>R. lauricola</i> and closely related, nonpathogenic fungal species are underway to elucidate modes of pathogenicity.

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