Efficacy of a biological control agent, Rhizobium vitis ARK-1, against grapevine crown gall in the United States
Mizuho Nita: Virginia Polytechnic Institute and State University
<div>Grapevine crown gall is an economically important disease impacting wine grape production around the world. Infection of grapevines by the bacterial pathogen <em>Rhizobium vitis </em>(=<em>Agrobacterium vitis</em>) leads to gall formation, girdling of the vascular system, and eventual vine death, due to the integration of Ti-plasmid segments into the host DNA, which causes hyperplasia of the host plant tissue. Because of the lack of an effective management method, crown gall is managed by removing the diseased vine and replanting with a healthy vine. However, this method does not completely remove the pathogen, which resides in plant debris in the soil. Recently, a new antagonistic <em>R. vitis </em>isolate (ARK-1) was found to prevent 90% of gall formation in grapevines infected with a pathogenic <em>R. vitis </em>isolate native to Japan<em>. </em>To test the efficacy of ARK-1 as a biological control agent against <em>R. vitis</em> isolates in the U.S., we conducted co-inoculation experiments with four Virginia native <em>R. vitis</em> isolates. Their pathogenicity was confirmed with PCR for the Ti-plasmid followed by an inoculation assay<em>. </em>ARK-1 and each pathogenic isolate were co-inoculated in 1:1 ratio to tomato or grapevines grown in the greenhouse. Two experiments revealed significant reductions (<em>P </em>< 0.05) in both gall incidence and size. Gall incidence in grape was reduced 77 to 100% and gall size was reduced 97 to 100%, indicating ARK-1 can be used as a tool for grapevine crown gall management in the US.</div>
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