EVALUATION OF GRAPEVINE ENDOPHYTIC BACTERIA FOR CONTROL OF PIERCES DISEASE

• Author(s): Kirkpatrick, Bruce; Wilhelm, Margot;
• Abstract: In this reporting period we optimized our antagonism assay using our previously known antagonists. We found that a Xylella fastidiosa (Xf) lawn with a concentration of 10(5)- 10(6) cfu/ml is optimal for visualizing zones of inhibition. Ten new isolates were shown to have antagonistic capability, including Bacillus subtilis, Pseudomonas sp., and Pantoea agglomerans. Fourteen isolates chosen for their antagonistic or competitive ability in vitro were assayed in planta for systemic movement. Of these isolates, six were able to move upwards 30cm from the point of inoculation. We continued our evaluation of Dr. Darjean-Jones initial biological control experiment started in 2003. During fall of 2005, xylem sap extracted from these vines with a pressure bomb yielded approximately 220 new isolates. Of these, 169 are from vines inoculated with isolate #169 Bacillus subtilis and isolate #161Bacillus sp. Eighty-five of our new isolates were sequenced and 44 of these are Bacillus sp. Nine isolates had the same sequence as the Bacillus species that was originally inoculated into the vines. In February, bud-wood from Dr. Darjean-Jones biological control experiment was collected from each treatment and propagated in the greenhouse. Ten vines per original treatment along with young Cabernet Sauvignon vines purchased from a nursery were inoculated with Staggs Leap strain of Xf in mid July, 2006. At 14 weeks post inoculation these vines will be assessed for Xf infection using Immunocapture (IC)-PCR and rated for Pierces disease symptom severity. A new biological control experiment was started in the greenhouse this spring. This experiment is comprised of seven endophyte treatments in 15 Thompson seedless vines per treatment. Vines were mechanically inoculated with the endophytes and 6 weeks later they were inoculated with Staggs Leap Xf. Xf infection and symptoms will be assessed after 14 weeks. We are testing the protective capabilities of three Bacillus sp. strains, three Pseudomonas strains, and one treatment co-inoculated with two Pseudomonas sp.
• Publication Date: Nov 2006
• Journal: 2006 Pierce's Disease Research Symposium