Location: Crop Germplasm ResearchTitle: Susceptibility of walnut and hickory species to Geosmithia morbida Author
|Grauke, Larry - L J|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2012
Publication Date: 5/1/2013
Citation: Utley, C., Nguyen, T., Roubtsova, T., Coggeshall, M., Ford, T.C., Grauke, L.J., Graves, A.D., Leslie, C.A., McKenna, J., Woeste, K., Yaghmour, M., Cranshaw, W., Seybold, S.J., Bostock, R.M., Tisserat, N. 2013. Susceptibility of walnut and hickory species to Geosmithia morbida. Plant Disease. 97(5):601-607. Interpretive Summary: Thousand cankers disease (TCD) of walnut is a very serious disease that is killing many black walnut trees (J. nigra) in the western United States. It is caused by a fungus (Geosmithia morbida) that infects thousands of feeding sites made by the walnut twig beetle (WTB), which spreads the disease. In 2010, TCD was discovered in the eastern U.S., where black walnut is a very valuable timber resource, and it has also been found in commercial walnut (J. regia) orchards in major production areas in California. The walnut genus (Juglans) is closely related to the hickory genus (Carya), which includes pecan. We tested the susceptibility of walnut and hickory species to G. morbida in greenhouse and field studies. All hickories tested were immune. All walnut species tested developed cankers, but some were much worse than others. J. nigra was the most susceptible. Arizona walnut (J. major) is a native host of the walnut twig beetle and possibly the fungus, and produced smaller disease spots (cankers). The size of the disease cankers was different depending on which tree was used as the male parent in controlled cross tests between black walnut and butternut (J. cinerea). This means that choosing the right parents for breeding may help make resistant trees.
Technical Abstract: Thousand cankers disease (TCD) of walnut is a result of feeding by the walnut twig beetle (WTB) and subsequent canker formation caused by Geosmithia morbida around galleries. TCD has caused extensive morbidity and mortality to J. nigra in the western United States and in 2010 was discovered in the eastern U.S., where black walnut is a highly valuable timber resource. WTB and G. morbida also have been found in J. regia orchards throughout major production areas in California, and the numbers of damaged trees that have been identified is increasing. We tested the susceptibility of walnut and hickory species to G. morbida in greenhouse and field studies. Carya illinoinensis, C. aquatica, and C. ovata were immune. All walnut species tested, including Juglans ailantifolia, J. californica, J. cinerea, J. hindsii, J. major, J. mandshurica, J. microcarpa, and J. regia developed cankers, although their susceptibility varied. J. nigra was the most susceptible, whereas J. major, a native host of the walnut twig beetle and presumably G. morbida, had smaller and more superficial cankers. Canker formation differed among maternal half-sibling families of J. nigra and J. cinerea, indicating genetic variability in resistance to G. morbida. J. regia developed cankers following inoculation with G. morbida, but its susceptibility varied considerably depending on experiment.