First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Silk Bay in Florida

• DOI: 10.1094/pdis-02-12-0149-pdn
• Publication Date: 2012-03-07T22:54:42Z
• Authors: M. A. Hughes; K. Shin; J. Eickwort; J. A. Smith
• Keywords: Frass; Persea

Silk bay (Persea humilis Nash) is a member of the Lauraceae precinctive to scrub forests central and southern Florida sister species primary laurel wilt host, redbay (P. borbonia (L.) Spreng), which generally not found in these ecosystems. In November 2011, observations silk mortality near Lake Placid Highlands County, FL, were reported Forest Service agents. A subsequent visit roadside homeowners' properties area revealed many dead dying silkbays with characteristic symptoms, including wilted crowns brown persistent foliage, frass accumulated at tree bases, sapwood dark streaking, ambrosia beetle entrance holes (1). Twig samples taken later confirmed as by Division Plant Industry Gainesville. Trunk from four trees for fungal isolation. Stem sections vascular discoloration surface disinfested 30 s 5% sodium hypochlorite solution then plated onto cycloheximide streptomycin malt extract agar (CSMA) All pieces resulted same cream-buff submerged growth pathogen Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva (2). DNA was extracted single-spore derived isolate, PL1389, an 18S small subunit ribosomal RNA gene sequence generated primers NS1 NS4, resulting 1,031-bp amplicon (3). BLASTn search showed identical homology R. strains PL159 PL382 (GenBank Accessions No. EU257806 JF797171, respectively, 100% similarity, e-value 0.0, total score 1,982). The deposited into GenBank assigned accession JQ247569. December spore suspension made flooding PL1389 culture plate 2 ml sterile water, collecting pipette, quantification adjusting 3.25 × 10 6 spores/ml hemacytometer. Pathogenicity tested on potted plants chamber experiment. Five bays three redbays drill-wounded 3/32” drill bit inoculated 20 μl suspension. Three two served water-inoculated controls. Within 5 weeks, all displayed disease, while controls remained healthy. Sapwood CSMA media. recovered only no asymptomatic bay, plays significant role limited ecosystems Florida, has now become another host epidemic, its implications upon yet be seen. References: (1) S. W. et al. Dis. 92:215, 2008. (2) Harrington Mycotaxon 104:399, (3) M. A. Innis PCR Protocols: Guide Methods Applications. Academic Press. San Diego, CA, 1990.