Abstract
Sap from hardwood stem pieces of five grape cultivars and 10 rootstock selections was collected by a water-displacement procedure and plated on a medium selective for the Agrobacterium tumefaciens biovar 3. Of 36 strains of A. tumefaciens recovered, 86% were identified as biovar 3 according to their physiological and virulence characteristics; 90% of the apical portions of grape canes sampled were free of A. tumefaciens. Our data provide the basis for a simple, yet rapid indexing system for the detection of low populations of unevenly distributed A. tumefaciens cells in grape wood. With this procedure, it should be possible to obtain A. tumefaciens-free propagating material.

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