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Walnut Research Conference 2020 Recap

The CWB’s production research program runs in an annual cycle culminating in the Walnut Research Conference held each year in late January. Following a call for research reports and proposals issued in late October – both with due dates in mid-December – the conference brings walnut researchers, farm advisors, and members of the CWB’s Production Research Committee together each winter to explore industry trends and production challenges, and to hear progr

ess reports on current CWB-funded projects and presentations of new project proposals. The conference convened for the 52nd time from January 29-31, 2020. The CWB Production Research Committee organizes production research into four main subject areas:

  • Walnut Breeding & Genomics

  • Orchard Management

  • Plant Pathology & Nematology

  • Entomology

The agenda is divided into four main sessions throughout the three-day conference and is structured to provide opportunities for formal and informal interaction among the attendees on key industry issues and research efforts designed to address them. Highlights of this year’s proceedings included: Among projects started in previous years and proposed to continue in 2020…

  • The walnut breeding program at UC Davis continues to make strides incorporating new marker-assisted breeding tactics to improve breeding efficiency and output for both varieties and rootstocks. Newly discovered markers for lateral bearing were used for the first time in 2019 to promptly eliminate the 30-50% of the progeny of the program’s cross-breeding efforts that normally turn out to be terminal bearers. Traditionally, these undesirable trees would have to be grown, maintained, and annually evaluated for expression of this and other traits – at considerable cost in time, effort, and land use.

  • The effort to breed new nematode, crown gall, Phytophthora, and Armillaria resistant walnut rootstocks – augmented, as with varieties, by new genetics-based selection approaches – is also moving forward at a rapid pace. Field evaluations of three to five “1st generation” new clonal rootstocks, alongside current seedling paradox and clonal “standards” RX1, VX211, Vlach continue at five regional trials planted in 2016. A second cohort of promising clonal candidates, some of which show superior resistance to multiple pests/diseases, are moving through the pipeline toward planting of additional field trials.

  • Allied efforts to identify genetic markers for other key variety and rootstocks traits for incorporation into the breeding program are making progress.

  • Work to validate the concept of delaying the start of irrigation season using tree water status readings as a water-saving and orchard health-improving strategy across varied orchard and site conditions is proving successful – and providing important new insights into how and when trees need and use water and the connection between irrigation practices and orchard productivity.

  • Early results from new research on kernel mold suggests that mold fungi establish early; unseen “latent” infections of hulls builds up by mid-summer which persist and develop into full-blown hull and kernel mold at harvest. Late summer fungicide sprays appear to be effective in stopping these infections and reducing kernel mold.

  • An entirely novel material and approach to controlling walnut blight appears to be emerging from efforts at UC Davis to better understand – and affect – the biochemical and genetic processes by which blight bacteria infect walnuts the mechanisms by which walnuts protect themselves.

  • The search for a navel orangeworm trap/lure combination that reliably tracks orchard NOW populations and, most importantly, accurately predicts the risk of harvest damage and need for treatment, continues.

Proposals for new projects to begin on 2020 included:

  • Development and use of new techniques to track and better understand navel orangeworm movement and migration among crops and across regions: where they originate, where and how far they move, and the role that other known (nut and non-nut) host crops play in their regional biology.

  • A proposal to “recycle and re-use” any fumigant that would be lost from chamber exhaust by capturing it with activated carbon filter and reusing it to fumigate single-tree orchard replant sites.

  • Evaluations of commercially available formulations of soil-applied, insect-attacking fungi for their potential to kill and control walnut husk fly – in the lab and, if successful there, in orchards.

  • A project to begin looking at whether it may be possible to breed new varieties less prone to rancidity without negative impacts on nut health and nutritional quality.

  • Evaluation of – and understanding the mechanisms involved in – the use of rest-breaking treatments to offset flowering, nut set and production impacts of low winter chilling.

The CWB’s Production Research Committee meets this year in mid-March to assess progress in continuing projects, consider proposals for new efforts, and to make funding decisions on both for formal Board action later this spring.


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