Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
University of California
Walnut Scion & Rootstock Improvement

Lethal Paradox

Lethal paradox canker (LPC) is manifested by multi-lobed, expansive bleeding bark cankers that originate below the soil surface and emanate up and around the Paradox trunk, producing profuse black exudation from the dead bark and resulting in tree death within 1 to 2 years. The etiology of LPC remains unknown.

Surveys of Disease Etiology

  • Complete statewide surveys of walnut orchards to characterize incidence of LPC. The disease has been found in 9 walnut-producing counties of California thus far.
  • Collect samples of necrotic bark from LPC cankers to isolate associated microorganisms and extract DNA for metagenomic analyses.
  • Conduct pathogenicity tests and complete Koch’s postulates with LPC-associated microorganisms.

Expected Outcomes

  • Threats posed by LPC will be identified.
  • Diagnostic protocols will be developed for use in orchard surveys to more fully assess risks posed by LPC to the California walnut industry.

Fig. 3. California counties with trees diagnosed with Lethal Paradox canker.

Fig. 1. Lethal Paradox canker.
Fig. 1. Lethal Paradox canker.
Fig 2. Lethal Paradox Canker: some bark removed.
Fig 2. Lethal Paradox Canker: some bark removed.

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