Budwood Transmission of Erwinia rubrifaciens, Causal Agent of Deep Bark Canker Disease of English Walnut. B. L. Teviotdale, Extension Plant Pathologist, University of California-Berkeley, Kearney Agricultural Center, Parlier 93648. G. S. Sibbett, L. Fitch, and D. H. Harper. Farm Advisor, Visalia, CA 93291; Former Farm Advisor, Yuba City, CA 95992; and Staff Research Associate, Kearney Agricultural Center, Parlier 93648. Plant Dis. 75:360-363. Accepted for publication 26 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0360.

Deep bark canker disease of English walnut (Juglans regia), caused by Erwinia rubrifaciens, was observed on 181 of 1,640 cv. Hartley trees in an orchard the first summer after planting. On most infected trees, external symptoms of disease were masked by subsequent growth and were not observed again until 5 yr later when 27 trees had symptoms. Of these 27 trees, 19 had symptoms in the first year. Three of 102 and one of 120 trees that grew from budwood collected from mature diseased trees and grafted to Northern California black walnut (J. hindsii) rootstock developed internal and external symptoms, respectively. In two experiments, the pathogen was recovered from four of 120 and 14 of 100 asymptomatic trees. Symptoms were not observed on trees grafted with budwood from healthy trees. Healthy budwood dipped or soaked in cell suspensions of the pathogen or cut with a contaminated knife was rejected when grafted, whereas noninoculated control grafts were successful.