Raffaelea lauricola sp. nov. (T.C. Harr. Fraedrich & Aghayeva)
Significance: A new vascular wilt of Lauraceae plant species has developed in the southeastern United States. The disease was first observed in Savannah, Georgia in 2003 and has since been reported in the lower coastal plains of South Carolina and northeastern Florida. Death of redbay (Persea borbonia) plants in these areas is attributed to a newly named fungus, Raffaelea lauricola sp. nov. This fungus was found in association with the exotic ambrosia beetle, Xyleborus glabratus Eichhoff. The disease has been observed on the following Lauraceae plants: swamp bay (Persea palustris or P. borbonia var. pubescens ), sassafras (Sassafras albidum), pondberry (Lindera melissaefolia), pondspice (Litsea aestivalis), camphor tree (Cinnamomum camphora) and avocado (Persea americana). Host range studies have also found susceptibility in spice bush (Lindera benzoin) and California bay (Umbellularia californica). Red maple, tulip poplar, and red oak were not found susceptible and testing with avocado gave inconsistent results. Nonetheless, avocado growers are concerned. The behavior of this fungus is similar to that of the Dutch elm disease pathogen, Ophiostoma novo-ulmi Brasier, where the pathogen moves systemically through the vessels of its hosts causing a vascular wilt. It is believed that the beetle and fungus were likely introduced via solid wood packing material.
Issues of Concern: This is the first report of an ambrosial fungus acting as an aggressive tree pathogen. The species is fast growing and is able colonize an entire tree from a single introduction point. Outside of the concern for the susceptibility of a commercially important crop like avocado, the host range includes plant species listed as threatened or endangered in the United States. Pondberry is listed as a federally endangered species while pondspice is considered a threatened species in some southeastern states. Already the loss of redbay in these southeastern coastal areas is extensive. Total loss of redbay could also impact a variety of associated plant and animal species such as the palamedes swallowtail butterfly (Papilio palamedes) which uses redbay as its primary host for larval development.
Fraedrich, S.W., T.C. Harrington, R.J. Rabaglia, M.D. Ulyshen, A.E. Mayfield III, J.L. Hanula, J.M. Eickwort, and D.R. Miller. 2008. A fungal symbiont of the redbay ambrosia beetle causes a lethal wilt in redbay and other Lauraceae in the southeastern United States. Plant Dis. 92: 215-224.
Harrington, T.C., S.W. Fraedrich, and D.N. Aghayeva. 2008. Raffaelea lauricola, a new ambrosia beetle symbiont and pathogen on the Lauraceae. Mycotaxon. 104: 399-404.
Mayfield, A.E. III. 2008. Laurel Wilt. Forest and Shade Tree Pests. Florida Department of Agriculture and Consumer Services, Division of Forestry. http://www.fl-dof.com/publications/fh_pdfs/Laurel_Wilt.pdf
USDA Forest Service. 2008. Laurel Wilt. USDA Forest Servcie, Forest Health Protection, Southern Region. http://www.fs.fed.us/r8/foresthealth/laurelwilt/index.shtml