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

Developing Disease Resistant Rootstock Integrating Conventional & Genomic Approaches

Project Summary

Most commercially cultivated walnut trees, grown for nut production, are grafted on rootstocks susceptible to root diseases that cause an estimated 18% annual yield loss. Availability of pathogen-resistant rootstocks is a critical need ranked by the walnut industry as its top research priority.

  • We will use an integrated approach encompassing plant propagation, disease resistance screening, genomics, and conventional breeding strategies to develop walnut rootstocks with resistance to four major soil-borne diseases of walnut caused by Agrobacterium tumefaciens, Phytophthora spp., Pratylenchus vulnus, and Armillaria mellea.
  • To accomplish this goal, we will exploit Juglandaceae germplasm collections in the USDA-ARS National Clonal Germplasm Repository in Davis and the Missouri Horticulture and Agroforestry Research Center. These collections will be used to identify genes conferring disease resistance. We then will develop molecular markers associated with these genes which will be used to identify resistant individuals in segregating populations. This will facilitate introgression of resistance traits into commercial rootstocks.
  • Emerging walnut rootstock diseases, such as Thousand Cankers disease and Lethal Paradox Canker disease will be monitored using an integrated research and outreach program.
  • Finally, a comprehensive economic analysis will optimize nursery propagation strategies and quantify the value to the industry of adopting pathogen-resistant clonal rootstocks developed here.

Our approach to developing disease resistant rootstocks

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