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Individual Highlight

Wingnut trees at risk to thousand cankers disease

Photo of Dark sap staining on the bark surface of a walnut tree (Pterocarya stenoptera) branch caused by underlying damage from the walnut twig beetle (Pityophthorus juglandis) and fungus (Geosmithia morbida) surrounding two beetle entrance or emergence holes. Dark sap staining on the bark surface of a walnut tree (Pterocarya stenoptera) branch caused by underlying damage from the walnut twig beetle (Pityophthorus juglandis) and fungus (Geosmithia morbida) surrounding two beetle entrance or emergence holes. Snapshot : The walnut twig beetle vectors a fungus that colonizes and kills the plant tissure known as phloem of walnut and butternut trees. Over the past two decades this condition, known as thousand cankers disease, has led to the widespread mortality of walnut trees (Juglans) in the U.S.. Recently the beetle and pathogen were discovered in three species of wingnut (Pterocarya) trees in the walnut family, in northern and southern California.

Principal Investigators(s) :
Seybold, Steven J. 
Research Location : California
Research Station : Pacific Southwest Research Station (PSW)
Year : 2017
Highlight ID : 1386

Summary

A multidisciplinary team of entomologists and plant pathologists led by Forest Service research entomologist Steve Seybold has discovered a new plant host for the organisms that cause thousand cankers disease. The disease has been characterized from walnut trees when the walnut twig beetle vectors a fungus, Geosmithia morbida Kola?ík, Freeland, Utley, and Tisserat (Ascomycota: Hypocreales), which colonizes and kills the phloem. Over the past two decades, thousand cankers disease has led to crown die back and the widespread mortality of Juglans tree species (walnut and butternut) in the U.S.. The team reported the occurrence of both the walnut twig beetle and G. morbida fungus in three wingnut species of walnut trees growing in the USDA National Clonal Germplasm Repository collection in northern California, and in the Los Angeles County Arboretum and Botanic Garden in southern California. Koch's postulates were satisfied with an isolate of G. morbida from the P. stenoptera species, confirming this fungus as the causal agent of thousand cankers disease in this host. A survey of the 37 Pterocarya Kunth accessions at the NCGR revealed that 46 percent of the trees had walnut twig beetle attacks or symptoms of G. morbida infection. This discovery suggests that the disease may threaten other tree species in the walnut family that may be of significance to urban forests.

Forest Service Partners

External Partners

 
  • Colorado State University
  • University of California at Davis