Identifying Environmental Sources of Agrobacterium Vitis in Vineyards and Wild Grapevines

Abstract

Agrobacterium vitis, the primary cause of grape crown gall, is known to survive internally in grapevines and be spread in propagation material. In this study we showed the bacterium can be detected in dormant grape buds as well as on surfaces of leaves collected from commercial vineyards. It was detected in as high as 90% of dormant bud samples and as high as 40% of leaf samples from individual vineyards using a highly selective and sensitive method based on magnetic capture hybridization together with real-time PCR. Highest percentages of detection occurred in samples collected from vineyards with high incidences of crown gall. A. vitis was also detected in 22% of wild grapevines (Vitis riparia) collected in New York and from 25% of feral grapevines that included V. californica, in California. Several of the vines sampled were growing more than 2 Km from commercial vineyards, demonstrating that wild grapevines can serve as a significant reservoir of inoculum. The specificity of the magnetic capture hybridization, real-time PCR assay used to detect tumorigenic A. vitis in the environment was further demonstrated by finding that 69 nontumorigenic strains from regions across the US did not amplify a virD2 PCR product.