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United States Department of Agriculture

Agricultural Research Service

Research Project: PROTECTION OF SUBTROPICAL AND TROPICAL AGRICULTURE COMMODITIES AND ORNAMENTALS FROM EXOTIC INSECTS Title: Laurel wilt: Understanding an unusual and exotic vascular wilt disease

Authors
item Ploetz, R -
item Smith, J -
item Pena, J -
item Hughes, M -
item Inch, S -
item Dreaden, T -
item Spence, D -
item Carrillo, D -
item Kendra, Paul
item Sankaran, S -
item Ehsani, R -
item Mayfield, Barbara
item Campbell, A -
item Hulcr, J -
item Stelinski, L -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 3, 2012
Publication Date: July 25, 2012
Citation: Ploetz, R., Smith, J., Pena, J., Hughes, M., Inch, S., Dreaden, T., Spence, D., Carrillo, D., Kendra, P.E., Sankaran, S., Ehsani, R., Mayfield, B.A., Campbell, A., Hulcr, J., Stelinski, L. 2012. Laurel wilt: Understanding an unusual and exotic vascular wilt disease. Meeting Abstract. 54th Annual Southern Forest Insect Work Conference; Charlottesville, VA; 24-27 July 2012.

Interpretive Summary: Laurel wilt kills American members of the Lauraceae plant family (Laurales, Magnoliid complex). These include significant components of Coastal Plain forest communities in the southeastern USA, most importantly redbay, as well as the commercial crop avocado. The disease has decimated redbay, swamp bay and silk bay; threatens rare members of the family with extinction; and causes major concern among avocado producers in California (no. 1 in USA, ca $350 million yr-1), Mexico (world’s top producer), and Florida (no. 2 in USA, ca $55 million yr-1), in which commercial production is now impacted. Laurel wilt is caused by Raffaelea lauricola, which has an Asian ambrosia beetle, Xyleborus glabratus, as a vector. In May 2002, X. glabratus was reported for the first time in the Western Hemisphere in Port Wentworth, GA. Laurel wilt has spread rapidly due to its mobile insect vector, the movement of infested wood, and the presence of native and non-native plants throughout the southeastern USA that are susceptible to the disease and on which the vector reproduces. As of January 2012, the western, northern and southern limits for laurel wilt were, respectively, 88.5oW, 35oN and 25.5oN. Despite campaigns against the indiscriminant movement of firewood, the disease’s discontinuous western and southern distributions indicate frequent anthropogenic activity. Laurel wilt is highly unusual. Ambrosia beetles are typically attracted to and colonize stressed or dead trees. Thus, the interaction of X. glabratus with healthy trees (i.e., before laurel wilt develops) is not normal. Furthermore, R. lauricola is an ambrosia fungus (nutritional symbiont) of X. glabratus; the beetle subsists on gardens of it, rather than wood, in infested trees. Since ambrosia fungi are usually saprobes that colonize no more than the walls of their brood galleries, the pathogenicity of R. lauricola is also atypical. Diverse strategies have been examined for managing laurel wilt, including host resistance (avocado and redbay), the use of fungicides (avocado and redbay), and insecticides and repellents (avocado). To date, no highly efficacious and cost-effective measure has been identified. In the absence of such a measure cultural methods, in particular the prompt identification, removal and destruction of infected/infested trees (sanitation), will play significant roles in disease mitigation. Ongoing work investigates a remote sensing method to replace molecular criteria that are used for disease diagnosis (i.e., to identify the pathogen in suspect trees). X. glabratus is attracted to volatiles produced by host and non-host plants, as well as its symbiont, R. lauricola. Field trials are elucidating the particular symbiont-derived attractants. Despite its rapid acropetal and basipetal movement in inoculated xylem, low concentrations of R. lauricola are evident in affected hosts. Microscopic localization of the fungus and its detection via DNA analyses is inconsistent, especially in avocado. Vascular function in avocado is dramatically reduced in affected avocado; reduced hydraulic conductivity and increased tylose blockage of xylem lumena are significantly correlated with increased external (wilting and foliar necrosis) and internal (sapwood discoloration) symptom development. Lethal disease develops in both avocado and redbay after inoculation with as few as 100 conidia of R. lauricola. The pathogen has been recovered from several species of scolytines that have been recovered from laurel wilt-affected avocado, redbay and swampbay. Compared to X. glabratus, fewer propagules of R. lauricola have been detected in these beetles (1,000s vs 100s or 10s). However, the rarity of X. glabratus in laurel wilt-affected avocado (no or very few individuals of this species are typically recovered) and what appear to be sufficient levels of inoculum in some of

Technical Abstract: Laurel wilt kills American members of the Lauraceae plant family (Laurales, Magnoliid complex). These include significant components of Coastal Plain forest communities in the southeastern USA, most importantly redbay, as well as the commercial crop avocado. The disease has decimated redbay, swamp bay and silk bay; threatens rare members of the family with extinction; and causes major concern among avocado producers in California (no. 1 in USA, ca $350 million yr-1), Mexico (world’s top producer), and Florida (no. 2 in USA, ca $55 million yr-1), in which commercial production is now impacted. Laurel wilt is caused by Raffaelea lauricola, which has an Asian ambrosia beetle, Xyleborus glabratus, as a vector. In May 2002, X. glabratus was reported for the first time in the Western Hemisphere in Port Wentworth, GA. Laurel wilt has spread rapidly due to its mobile insect vector, the movement of infested wood, and the presence of native and non-native plants throughout the southeastern USA that are susceptible to the disease and on which the vector reproduces. As of January 2012, the western, northern and southern limits for laurel wilt were, respectively, 88.5oW, 35oN and 25.5oN. Despite campaigns against the indiscriminant movement of firewood, the disease’s discontinuous western and southern distributions indicate frequent anthropogenic activity. Laurel wilt is highly unusual. Ambrosia beetles are typically attracted to and colonize stressed or dead trees. Thus, the interaction of X. glabratus with healthy trees (i.e., before laurel wilt develops) is not normal. Furthermore, R. lauricola is an ambrosia fungus (nutritional symbiont) of X. glabratus; the beetle subsists on gardens of it, rather than wood, in infested trees. Since ambrosia fungi are usually saprobes that colonize no more than the walls of their brood galleries, the pathogenicity of R. lauricola is also atypical. Diverse strategies have been examined for managing laurel wilt, including host resistance (avocado and redbay), the use of fungicides (avocado and redbay), and insecticides and repellents (avocado). To date, no highly efficacious and cost-effective measure has been identified. In the absence of such a measure cultural methods, in particular the prompt identification, removal and destruction of infected/infested trees (sanitation), will play significant roles in disease mitigation. Ongoing work investigates a remote sensing method to replace molecular criteria that are used for disease diagnosis (i.e., to identify the pathogen in suspect trees). X. glabratus is attracted to volatiles produced by host and non-host plants, as well as its symbiont, R. lauricola. Field trials are elucidating the particular symbiont-derived attractants. Despite its rapid acropetal and basipetal movement in inoculated xylem, low concentrations of R. lauricola are evident in affected hosts. Microscopic localization of the fungus and its detection via DNA analyses is inconsistent, especially in avocado. Vascular function in avocado is dramatically reduced in affected avocado; reduced hydraulic conductivity and increased tylose blockage of xylem lumena are significantly correlated with increased external (wilting and foliar necrosis) and internal (sapwood discoloration) symptom development. Lethal disease develops in both avocado and redbay after inoculation with as few as 100 conidia of R. lauricola. The pathogen has been recovered from several species of scolytines that have been recovered from laurel wilt-affected avocado, redbay and swampbay. Compared to X. glabratus, fewer propagules of R. lauricola have been detected in these beetles (1,000s vs 100s or 10s). However, the rarity of X. glabratus in laurel wilt-affected avocado (no or very few individuals of this species are typically recovered) and what appear to be sufficient levels of inoculum in some of these beetles to cause disease raise the possibility that species other than X. glabratus are also vectors. Ongoing work investigates this possibility on avocado and redbay. Other means by which the pathogen could be transmitted include movement via root grafts (probable), pruning equipment (less likely), and avocado fruit, seed and scion material (doubtful).

Last Modified: 10/30/2014
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