Biocontrol of Pierce's disease of grapevine and citrus greening with a benign strain of Xylella fastidiosa
Vascular diseases caused by xylem-limited Xylella fastidiosa subspp. and phloem-limited Candidatus Liberibacter spp. result in large economic losses in many agricultural plants. X. fastidiosa is rapidly spreading into new hosts and areas. Except for plant resistance, there is no effective control for these diseases. In a trial established in the UC Riverside vineyard in 2011, a pin-pricking technique was used to inject a benign strain of X. fastidiosa (EB92-1) into the xylem vessels of Pinot Noir and Cabernet Sauvignon grapevines in the greenhouse prior to transplanting into the vineyard. Under heavy disease pressure, EB92-1 has provided control of Pierce’s disease (PD) for 6 years in Cabernet Sauvignon and Pinot Noir. Compared to only 10% of the treated vines, 40 percent of the untreated vines had severe PD symptoms. None of the treated vines have died; whereas, 10% of the untreated have died. Trials were established in Florida in 2014 to evaluate EB92-1 for prevention of citrus greening symptoms. A power drill and syringe were used to inject the biocontrol strain into the tree. After 3 years, 53% of the untreated, mature trees were dead or dying from citrus greening, compared to only 10% of the treated. In young trees, there were moderate symptoms in 18% of the untreated and in 5% of the treated. Biological control of diseases caused by X. fastidiosa, and possibly Candidatus L. subspp., with a benign strain of X. fastidiosa, EB92-1, may be feasible.