Populations of Agrobacterium in Vineyard and Nonvineyard Soils and Grape Roots in Vineyards and Nurseries

Abstract

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.