Xyleborus glabratus attacks and systemic colonization by R affaelea lauricola associated with dieback of C innamomum camphora in the southeastern U nited S tates

• Published in: Forest pathology = Journal de pathologie forestière = Zeitschrift für Forstpathologie 2015-02, Vol.45 (1), p.60-70
• Main Authors: Fraedrich, S. W., Harrington, T. C., Best, G. S.
• Format: Article
• Language: English
• ISSN: 1437-4781; 1439-0329
• DOI: 10.1111/efp.12124

Laurel wilt, caused by R affaelea lauricola , is responsible for extensive mortality of redbay and other A merican members of the L auraceae in the southeastern U nited S tates. Raffaelea lauricola is a mycangial symbiont of the redbay ambrosia beetle ( X yleborus glabratus ), and the beetle and fungus were accidentally introduced from A sia. Branch dieback of camphortree ( C innamomum camphora ), an A sian member of the L auraceae, has been occasionally observed in areas where laurel wilt has decimated redbay populations, and R . lauricola was isolated from such camphortrees. However, the role of X . glabratus and R . lauricola in this branch dieback remains unclear. Examination of camphortrees on J ekyll I sland, G eorgia showed that healthy‐appearing trees and those with branch dieback had been attacked by X . glabratus , but the trees with branch dieback had four times as many beetle attacks. Raffaelea lauricola was routinely isolated from discoloured xylem near beetle tunnels in healthy trees and those with dieback. Single‐point inoculations with R . lauricola on stems of mature, healthy camphortree trees failed to induce wilt‐like symptoms or branch dieback, although areas of discoloration were scattered throughout the xylem, and R . lauricola was reisolated irregularly at various heights in some inoculated trees. In growth chamber experiments, single‐point inoculations with R . lauricola resulted in systemic colonization but no wilt symptoms or branch dieback in camphortree saplings. In contrast, inoculations at multiple points along the stem (simulating multiple attacks by the vector) caused branch dieback and wilt‐like symptoms, including a brownish, diffuse discoloration of the xylem. Camphortree appears to be more resistant than A merican species of L auraceae to the vascular wilt caused by R . lauricola . The fungus does colonize camphortrees systemically, however, and can apparently cause branch dieback. This suggests that the fungus may provide brood material for X . glabratus in A sia as it does in the southeastern U nited S tates.