Populations of Agrobacterium in Vineyard and Nonvineyard Soils and Grape Roots in Vineyards and Nurseries. T. J. Burr, Associate Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. B. H. Katz, and A. L. Bishop. Technician, and Postdoctoral Associate, Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456. Plant Dis. 71:617-620. Accepted for publication 13 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0617.

Higher populations of biovar 3 of Agrobacterium tumefaciens and A. radiobacter were isolated from roots of grapevines with crown gall than from roots of noninfected vines or from nonrhizosphere soils sampled from infected and noninfected vineyards. Biovar 3 was not detected by plating serial dilutions of nonvineyard soils on a selective medium, indicating that populations were less than 100–1,000 colony-forming units per gram of soil. Roots of apparently healthy rootstocks and nongrafted grapevine cultivars sampled from nursery storages were contaminated with tumorigenic and nontumorigenic biovar 3. When specific sections of roots were assayed for biovar 3, it was predominantly isolated from small, dark, sunken lesions on the roots.