Variable Response of Bacteria Isolated From Grapevine Xylem to Control Grape Crown Gall Disease in planta

Abstract

A total of 851 bacterial isolates from the xylem sap of grapevines grown in Nova Scotia, Canada, were purified and screened for in vitro antagonistic activity against a range of tumorigenic A. tumefaciens biovar 3 strains (A. vitis). Despite vagaries noted in performing in vitro antibiosis, 24 strains were catalogued as having a strong inhibitory effect on A. vitis. Biolog plates identified this collection of 24 as 35% Enterobacter agglomerans, 30% Rahnella aquatilis, and 35% Pseudomonas spp. Soil microcosm studies with a xylE marked A. vitis strain showed that one of these endophytes (an isolate of P. corrugata) was able to control population numbers of the agrobacteria in situ. In planta trials with V. vinifera cv. Chardonnay, where less than 47% of the positive control treatment produced galled vines, demonstrated significant biocontrol of the disease by three of the endophytes. Trials with Gewürztraminer vines, with a successful infection of > 88% with the positive control, showed no biocontrol. Experiments attempting to introduce three of the most inhibitory endophytes into Gewürztraminer vines also failed. However, it was possible to introduce the virulent A. vitis strain CG64 into these vines by applying bacterial suspension to unwounded stems.