Progress 08/01/09 to 07/31/11
Outputs
OUTPUTS: Black walnut (Juglans nigra) is one of the most valuable hardwoods harvested in the eastern United States. Since 2001 widespread mortality of black walnut has been reported throughout the western United States. Mortality is the result of a combination of an expanded geographic range of the walnut twig beetle (Pityophthorus juglandis), its aggressive feeding behavior on black walnut, and extensive cankering caused by a newly described fungus, Geosmithia morbida, associated with the beetle. Thousand cankers disease is eliminating black walnut in many regions of the West and was recently found in Tennessee, Virginia and Pennsylvania. It now poses a grave risk to this species in its native range in eastern North America. Our objective was to screen walnut and related hickory species for susceptibility to TCD and to look for potential sources of resistance. In 2010, we determined that black walnut was highly susceptible to the fungus and cankers were always produced on this host. In contrast pecan and shagbark hickory were immune. Other walnut species appear moderately resistant to highly resistant to canker formation relative to black walnut. In 2011, we found that there were differences in canker sizes in black walnut half-sibling families following inoculation with G. morbida. Cankers in some half-siblings were approximately half the size of the most susceptible families, suggesting that resistance to the fungus may be present in the population. Surviving black walnuts have been observed in Boulder Colorado in neighborhoods where thousand cankers disease was epidemic. We also determined that canker sizes in black walnut families were influenced by temperature, with larger cankers formed at 25C compared to 32C. All G. morbida haplotypes tested were similar in aggressiveness. PARTICIPANTS: M. Coggeshall, University of Missouri, K. Woeste USDA Forest Service, and T. Ford, Improving Perennial Plants for Food and Bioenergy provided germplasm material for thousand cankers disease screening. Whitney Cranshaw, Professor Bioagricultural Sciences and Pest Management at Colorado State University participated in all monitoring efforts and was instrumental in collecting samples in the southwestern United States During the year, we provided numerous trainings (International Society of Arboriculture, Schatz tree genetics symposium Pennsylvania, Walnut Council meeting Purdue, Northern Nut Growers meeting Utah, National Plant Diagnostic Network meeting California, Western Forest Insect Work group, Oregon, and several online training sessions) reaching over 1000 participants. TARGET AUDIENCES: Our target audiences included arborists, forest pest researchers, university personnel. Following the online training session over 90% of participants indicated that they had learned about the symptoms of TCD and susceptibility of walnut species to the disease. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The results of our inoculation trials demonstrate that black walnut is highly susceptible to canker formation following inoculation with the fungus Geosmithia morbida. Unfortunately the appearance of thousand cankers disease in the native range of black walnut in 2010 now poses a serious threat to the black walnut industry, with an estimated total value of half a trillion dollars. Nevertheless, we have demonstrated that there is genetic variation in susceptibility of black walnut to Geosmithia morbida and this may be useful in gerplasm preservation or breeding programs. Other walnut species appear to be less affected by the fungus. For example, Arizona walnut is highly resistant; this species appears to be the native host of the beetle and fungus and might be used in breeding programs. English walnut is moderately resistant and thousand cankers disease does not currently appear to be a major threat to the $500M per year English walnut industry in California. However, there were several reports of thousand cankers disease in English walnuts and hybrid walnut rootstocks in a few California orchards. Continued screeing of English walnut rootstock is warranted. Our research has demonstrated that Carya species are immune to thousand cankers disease. Thus the North American pecan industry will likely not be impacted by thousand cankers disease.
Publications
- Tisserat N., Cranshaw W., Putnam, M., Pscheidt, J. Leslie, C.A., Murray, M., Hoffman, J., Barkely, Y., Alexander, K., and Seybold, S.J. 2011. Thousand cankers disease is widespread on black walnut, Juglans nigra, in the western United States. Online. Plant Health Progr. (June 30, 2011) doi:10.1094/PHP-2009-0811-01-RS.
- Kolarik, M., Freeland, E., Utley, C. and Tisserat, N. 2011. Geosmithia morbida sp. nov., a new phytopathogenic species living in symbiosis with the walnut twig beetle (Pityophthorus juglandis) on Juglans in the USA. Mycologia 103:325-332.
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Progress 08/01/09 to 07/31/10
Outputs
OUTPUTS: Black walnut (Juglans nigra) is one of the most valuable hardwoods harvested in the eastern United States. Since 2001 widespread mortality of black walnut has been reported throughout the western United States. Mortality is the result of a combination of an expanded geographic range of the walnut twig beetle (Pityophthorus juglandis), its aggressive feeding behavior on black walnut, and extensive cankering caused by a newly described fungus, Geosmithia morbida, associated with the beetle. We have named the disease thousand cankers (TCD) because mortality is the result of bark necrosis caused by an enormous number of coalescing branch and trunk cankers. Thousand cankers disease is eliminating black walnut in many regions of the West and was recently found in Tennessee. It now poses a grave risk to this species in its native range in eastern North America. Our objective was to screen walnut and related hickory species for susceptibility to TCD and to look for potential sources of resistance. One-year-old trees were inoculated in the greenhouse. Field inoculations of Juglans and Carya species were conducted at the Center for Improving Perennial Plants for Food and Bioenergy (IPPFB) headquartered in Richmond UT. Results of the greenhouse and field inoculation experiments, in general were consistent with field observations. Juglans nigra was highly susceptible to the fungus and cankers were always produced on this host. In contrast pecan and shagbark hickory were immune. Other walnut species appear moderately resistant to highly resistant to canker formation relative to black walnut . These results corroborate field observations. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The results of our inoculation trials demonstrate that black walnut is highly susceptible to canker formation following inoculation with the fungus Geosmithia morbida. Other walnut species appear to be less affected by the fungus. For example, Arizona walnut is highly resistant; this species appears to be the native host of the beetle and fungus. English walnut is moderately resistant and TCD does not currently appear to be a major threat to the $500M per year English walnut industry in California. Similarly the North American pecan industry will likely not be impacted by TCD. Moderately to highly resistant walnut species including little walnut and Arizona walnut could be sources of resistance in future breeding programs.
Publications
- No publications reported this period
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