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United States Department of Agriculture

Agricultural Research Service

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Location: Crop Germplasm Research

2010 Annual Report

1a. Objectives (from AD-416)
We propose to use greenhouse inoculations to evaluate the susceptibility of Juglans and Juglandaceae germplasm to Thousand Cankers disease. The immediate goal is to evaluate the potential risk posed by Thousand Cankers disease to NCGR core collections in Davis, Corvallis, and Somerville. All data, including information concerning variation in resistance within species will be communicated to the NCGR curators who will add it to the GRIN database. They may also choose to: 1) Pursue funding for additional evaluation of susceptible species and families within existing collections; 2) Begin additional research related to protection of existing collections where necessary; 3) Begin evaluation of the need to backup existing collections if they are threatened by Thousand Cankers disease; and 4) Add genotypes to their collections if useful variability in susceptibility is detected.

1b. Approach (from AD-416)
One–year-old woody seedlings (1-0 nursery stock or its equivalent) of J. californica, J. nigra, J. regia, J. ailantifolia, J. cinerea, J. major, J. hindsii, J. microcarpa, Paradox rootstocks, C. illinoinensis, C. aquatic, C. ovata, and C. texana approximately 0.5-1 cm diameter at ground level will be used for pathogenicity tests. J. major is included in the study as a control, since it is a host for P. juglandis but is not usually killed by Geosmithia. Dormant trees will be planted in 3.8-liter pots in a commercial nursery mix and placed in a greenhouse at Colorado State University. Inoculations will be made after the trees resume growth and leaves have fully emerged. Two isolates each of Geosmithia will be grown for 10 days on 1/2 strength PDA. Inoculations will be made by slicing down through the bark with a sterile scalpel at three sites on each stem. Resulting wounds are approximately 0.5-1.0 cm wide and 1 cm long with the flap of bark still attached to the stem at the base of the wound. A plug of sterile 1/2 strength PDA approximately 0.5 cm2 will be inserted under the bark flap and against the wood on the middle wound on each tree. An agar plug of similar size but colonized by one of the fungal isolates will then be inserted under the bark flap on the top and bottom wound. Four to 18 trees of each taxa will be inoculated with each isolate. All wounds will be sealed with Parafilm(R) and the trees will be randomly placed on a greenhouse bench. The Parafilm(R) will be removed after 3 wk. After 8 wk, all trees will be harvested and the outer bark shaved from the wounds with a sterile scalpel to expose the extent of bark colonization. The length and area of discolored tissue will be recorded and compared to cankers on the susceptible J. nigra and the control species J. major. If there are space, labor, or time constraints in the completion of the research, the cooperator will consult with the chair of the Juglans CGC and the other PIs to determine how many trees of each species to inoculate and evaluate. The goal will be to obtain clean, replicated data from as many taxa as possible, with priority given to those genotypes currently in NCGR repositories.

3. Progress Report
This is a new project, with the goal of evaluating the susceptibility of Juglans (walnut) and Carya (pecan and hickory) germplasm to thousand cankers disease. One- to three-year old potted seedlings of 10 species of Juglans or Carya were inoculated with two isolates of the microorganism that causes the disease. Discolored bark due to disease damage was measured after 6 weeks. The Juglans species tested varied in susceptibility to the disease organism, with Juglans nigra (black walnut) being the most susceptible and Juglans hindsii and Juglans major being the least susceptible. Other Juglans species also developed disease symptoms (cankers) following inoculation. The susceptibility of Juglans californica to thousand cankers was consistent with recent reports of decline of that species in southern California associated with the disease. The susceptibility of Juglans microcarpa as shown by this work is of concern because the native range of this species in New Mexico, Texas, Oklahoma, and Kansas could serve as a bridge for movement of the disease-causing fungus and the beetle that transmits it into the native range of Juglans nigra, which is an important commercial U.S. tree providing high quality walnut lumber for cabinetmaking, etc. Although canker development was observed on Juglans regia, natural infection of this species has only rarely been observed in Colorado, Utah, and California. Carya illinoinensis and Carya ovata were shown by project work to be not susceptible to the thousand cankers fungus. Ongoing work by this project will develop valuable information concerning the susceptibility of important native U.S. trees to the devastating effects of disease organisms transmitted by insects. The ADODR of this project and the cooperator maintain regular communication by phone and e-mail, where progress of the work is discussed and evaluated, and where solutions to work impediments are developed. The ADODR and the cooperator periodically meet face-to-face (at national scientific meetings, etc.) to discuss research priorities and the overall direction and progress of the work. This project was scheduled to expire in FY 2010 but was extended through 06-30-2012.

4. Accomplishments

Last Modified: 06/26/2017
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