Written by Corina Serban, WSU Extension; Reviewed by Scott Harper, WSU Plant Pathology, Jessica Kohntopp, Ruff Country K9 LLC. December 6, 2024
Introduction
Little Cherry Disease (LCD) is caused by three pathogens – Little Cherry Virus-1 (LChV-1), Little Cherry Virus-2 (LChV-2), and X-disease phytoplasma (XDP) and poses a serious threat to cherry orchards. Once a tree is infected, there is no cure making early detection critical to prevent the pathogen spread and economic losses. Trees can serve as a source of infection for years before showing visible symptoms in their fruit. Currently, the primary detection methods include visual scouting (1-2 before harvest) and molecular assays like qPCR. However, visual scouting cannot detect early infections, and while qPCR is highly accurate, it is costly, labor-intensive, and limited by the pathogen’s patchy distribution in tree tissue. To address these challenges, Washington State University (WSU) in collaboration with Ruff Country K9 LLC, is exploring a groundbreaking solution: using trained detection dogs to identify trees infected with LCD pathogens.
Project Overview
This ongoing research project, funded by the Washington Tree Fruit Research Commission and Northwest Nursery Improvement Institute (May 2023 – May 2025), has four primary objectives:
- Train Canines: Train two dogs to detect LCD pathogens (LChV-2, XDP)
- Validation: Assess the canines’ accuracy, sensitivity, and specificity in controlled studies, with a goal of achieving 95% accuracy or higher before advancing to field settings
- Field Introduction: Transition canines to mock field setting for real-world applicability
- Expanded Studies: Conduct dormancy, temporal, nursery study, and orchard evaluations
Key Findings
Training and Validation
- The trained canines demonstrated odor discrimination of the two pathogens and were proofed off of other diseases common in cherry orchards, ensuring specific alerts to LCD pathogens.
- Sensitivity to pathogen titers ranged from low 39 (XDP), 36 (LChV-2) and as high as 18 (XDP and LChV-2).
Controlled Studies
- In a blind greenhouse study, canines successfully identified 7 positive potted trees, and one additional tree later confirmed positive by qPCR.
- Blind study results:
- Accuracy: 99.72 %
- Sensitivity: 96%
- Specificity: 100%
- Notably, initial testing showed some missed alerts due to canine illness (heat exhaustion). A follow-up study showed significant improvement, particularly for Aika (Table 1).
Field Transition
- The canines adapted successfully to mocked field scenarios, detecting positive trees in mapped grids. Both canines have been alerting on the positive trees and have not shown any change in behavior towards any other tree.
- In a young commercially cherry orchard with one tree known to be positive, canines flagged 21 trees. Subsequent testing confirmed 4 additional positive trees with weak infections (titer levels 37.63 – 39.41).
- In an older commercially cherry orchard, with trees flagged at harvest for visual symptoms, canines have alerted on 4 trees; subsequent testing confirmed 3 of them positive (titer levels 33.58 – 39.66).
Dormancy and Seasonal Studies
- Initial runs on dormant trees (November 2024) revealed that the canines accurately located all 4 known qPCR-positive trees and flagged an additional 51 trees for testing in 2025.
Next Steps
- Conduct qPCR testing on flagged trees from dormancy studies and retest the previous trees that the canines flagged during the season to validate the accuracy of the canines.
- Expand field studies to additional orchard blocks.
- Deep dive into the canines’ capabilities in a nursery setting.
Table 1. Blind Study Results
Blind Study Results
| Initial Blind Study | Mini Study | ||
|---|---|---|---|
| Canine | Humma | Aika | Both Canines |
| Sensitivity | 95.05% (96/101) | 88.12% (89/101) | 96% (48/50) |
| Total Positives Missed | 5 | 12 | 2 |
| Specificity | 100% (1279/1279) | 100% (1279/1279) | 100% (670/670) |
| Total Negative Missed | 0 | 0 | 0 |
| Positive Predictive Value | 100% | 100% | 100% |
| Negative Predictive Value | 99.61% | 99.07% | 99.70% |
| False Positive Rate | 0.00% | 0.00% | 0.00% |
| False Negative Rate | 4.95% | 11.88% | 4.00% |
| False Discovery Rate | 0.00% | 0.00% | 0.00% |
| Accuracy | 99.64% (1375/1380) | 99.13% (1368/1380) | 99.72% (718/720) |
Footnotes: Accuracy: The total number of correct alerts on positive trees and non-alerts on negative trees. Sensitivity: The total amount of correct alerts on positive trees. Specificity: The total amount of correct non-alerts on negative trees.
Figure 1. Humma alerting on a potentially infected tree with LCD pathogens (November 2024)
Figure 2. Aika alerting on a potentially infected tree with LCD pathogens (November 2024)
To read more in detail about the project’s preliminary findings see below the link to the WTFRC continuing report.
Contact
Name: Corina Serban
Affiliation: WSU Extension
Email: corina.serban@wsu.edu
Phone: (509) 574-1595
Name: Scott Harper
Affiliation: WSU Plant Pathology
Email: scott.harper@wsu.edu
Phone: (509) 786-9232
Name: Jessica Kohntopp
Affiliation: Ruff Country K9 LLC (Owner)
Email: jesskohntopp@gmail.com
Phone: (208) 602-1293
Funding and Acknowledgments
Project Team: Jessica Kohntopp (Ruff Country K9 LLC); Co-PI: Corina Serban (WSU Extension); Co-PI: Scott Harper (WSU)
Collaborators: Cody Molnar (WSU), Teah Smith (Zirkle Fruit Company), Craig Harris (Harris Farms), Daisy Arias (Stemilt Growers LLC), Bill Howell (NNII), Todd Cameron (Cameron Nursery), Garrett Bishop (G.S Long Company), Rodney Cooper (USDA-ARS)
Funding Sources: Washington Tree Fruit Research Commission, Northwest Nursery Improvement Institute
Additional Information
X-disease phytoplasma (Western X)
BMPs for tree removal for X-disease and Little Cherry Virus infected trees
Alternative weedy hosts for X-disease phytoplasma. Fruit Matters March 2024
Clarke, A.E., Catron, K.A., Reyes Corral, C., Marshall, A.T., Adams, C.G., Cooper, W.R., Harper, S.J., Nottingham, L.B., Northfield, T.D., 2024. Colladonus spp. (Hemiptera: Cicadellidae) vectors of X-disease: biology and management in Western United States. Journal of Integrated Pest Management 15.
Harper, S.J., Northfield, T.D., Nottingham, L.B., DuPont, S.T., Thompson, A.A., Sallato, B.V., Serban, C.F., Shires, M.K., Wright, A.A., Catron, K.A., Marshall, A.T., Molnar, C., Cooper, W.R., 2023. Recovery Plan for X-Disease in Stone Fruit Caused by ‘Candidatus Phytoplasma pruni’. Plant Health. Prog. 24, 258-295.
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