Location: Crops Pathology and Genetics Research
Project Number: 2032-22000-017-078-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2026
End Date: Aug 31, 2030
Objective:
Phytophthora root and crown rot, crown gall, and plant-parasitic nematodes represent significant constraints to walnut production in California, resulting in tree decline, mortality, reduced water-use efficiency, and substantial yield losses. Current management practices depend primarily on preplant soil fumigation and chemical treatments, which pose both economic and environmental challenges. The proposed project seeks to evaluate RNA interference (RNAi)-based genetic resistance as a sustainable alternative for disease management.
Approximately 60 transgenic walnut embryo lines carrying RNAi constructs targeting these pathogens have been generated. The primary objective of this project is to screen and identify transgenic walnut rootstock lines that exhibit enhanced resistance to Phytophthora, crown gall, and nematodes under controlled laboratory conditions. Tissue culture-based pathosystems will be employed to provide reproducible, rapid, and cost-effective methods for evaluating disease resistance. Promising lines will subsequently be advanced for field evaluation.
Successful completion of this project will result in the identification of candidate walnut rootstocks with broad-spectrum resistance to multiple soilborne pathogens, thereby reducing reliance on fumigants and pesticides and enhancing the sustainability of walnut production. Project success will be measured by the identification and validation of transgenic walnut rootstock lines demonstrating significantly improved resistance to multiple target pathogens.
Approach:
Approximately 60 transgenic walnut embryo lines have already been developed and are being maintained and propagated through tissue culture. In vitro-regenerated shoots and roots will be used to evaluate resistance to crown gall, Phytophthora root and crown rot, and plant-parasitic nematodes using established laboratory bioassays. Disease severity, pathogen colonization, and plant growth performance will be quantified and compared with non-transgenic controls. Transgenic lines exhibiting enhanced resistance will be advanced for further testing, validation, and eventual field evaluation.