EVALUATION OF GRAPEVINE ENDOPHYTIC BACTERIA FOR CONTROL OF PIERCES DISEASE

• Author(s): Kirkpatrick, Bruce; Whistler, Cheryl; Wilhelm, Margot;
• Abstract: We continued to screen our endophyte library for in vitro antagonism of Xylella fastidiosa (Xf) growth. Approximately 16 isolates exhibited antagonism out of the 150 strains that were screened. To date, we have screened approximately 650 isolates and identified 66 that showed some level of Xf-antagonism. We are continuing to screen the rest of the library and will conduct grapevine movement assays on all antagonists in the coming year. Greenhouse testing of six grapevine endophytes that began in 2003 showed that three isolates provided statistically significant reduction in Pierces disease (PD) symptom severity. Five months after these vines were removed from the greenhouse and planted in the field, all but one of the non-protected, Xf-inoculated, positive control vines were dead or had PD symptoms. No symptoms were observed in any of the ten vines that were inoculated with a Cellulomonas endophyte nor eight of ten vines inoculated with a Bacillus spp. These results indicate that these two endophytes have the ability to suppress populations of Xf within grapevines, because these vines initially tested positive for Xf four months following inoculation nor after transplanting these vines in the field. A large greenhouse biocontrol experiment involving four of the Pseudomonads, or combinations of the Pseudomonads with Pseudomonas viridiflava to act as a movement facilitator, were established in August 2004. Unfortunately it appears that there was a low efficiency of inoculation using blue-green sharpshooters (BGSS) as well as mechanical inoculation because PD symptoms were not evident on the positive control vines four months following inoculation. The vines will be rated again for symptoms and planted in the field, which may help to induce PD symptoms. Additional endophytes were isolated from escape vines; i.e. vines without apparent symptoms in vineyards with large PD losses on two occasions in Fall 2004. Representative colonies were grown in liquid media and stored at -80C. During 2005 these isolates, as well as others from the original endophyte library will be screened for Xf-antagonism in vitro.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium