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United States Department of Agriculture

Agricultural Research Service

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Location: Crop Germplasm Research

2012 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:
The goal of this project is to evaluate the susceptibility of Juglans and Juglandaceae (walnut) germplasm to Thousand Cankers disease (TCD). This disease infects walnut trees and can result in tree death. In FY 2012, publication of research accomplished by this project was completed, including the affirmation that no evidence of TCD was found in Texas native walnuts, and no species of Carya tested showed susceptibility to the TCD fungal disease agent Geosmithia morbida. Results suggest the need for testing of black walnut across its range for susceptibility to TCD, including native populations in Texas. Work by this project, overall, is important for the contribution it has made to the recognition in native tree species of susceptibility to TCD and likely other potentially devastating diseases vectored by resident insect populations. Project work may ultimately facilitate development of new procedures and protocols that will help prevent the spread of disease-carrying pests to associated orchard crops. This project expired in FY 2012.

4. Accomplishments

Last Modified: 06/22/2017
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