BIOLOGICAL-CONTROL OF CROWN GALL IN GRAPEVINE AND RASPBERRY BY 2 PSEUDOMONAS SPP. WITH A WIDE SPECTRUM OF ANTAGONISTIC ACTIVITY

Pseudomonas aureofaciens B-4117 and P. fluorescens CR330D inhibited th e growth of a wide range of plant pathogens, including Agrobacterium t umefaciens, when tested on agar media. In a series of nursery-based tr ials with natural pathogen inoculum, application of either B-4117 or C R330D significantly reduced the incidence and severity of crown gall c aused by A. tumefaciens on grapeville and raspberry. The extent of dis ease control depended upon the variety tested. Both bacteria reduced d isease during seedling root production and grafting. The disease incid ence on root cuttings of three grapevine varieties was reduced by 56-8 0% and the disease severity index (DSI) was decreased by 75-86%. Depen ding on the scion variety, the number of healthy rooted grafts increas ed by 2-3.5-fold, while the DSI was reduced by 1.5-3-fold. The results suggest that there is potential in using these antagonists to diminis h the influence of latent rootstock infection on graft sensitivity to crown gall. Pretreatment of rooted raspberry seedlings with P. aureofa ciens B-4117 prevented the development of crown galls caused by A. tum efaciens strain K24 or by a mixture of A. tumefaciens pathogenic strai ns previously isolated from raspberry. Both Pseudomonas spp. persisted on the root surfaces of inoculated vine cuttings and in non-sterile s oil. The advantages of using the antagonistic bacteria as biocontrol a gents of crown gall are discussed.