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Biological Control for Grapevine Crown Gall by Nonpathogenic Rhizobium vitis Strain ARK-1

Akira Kawaguchi: Westen Region Agricultural Research Center, NARO

<div>Crown gall of grapevine, which is caused by tumorigenic <em>Rhizobium vitis</em>, is the most important bacterial disease of grapevine throughout the world. Screening tests of biological control agent resulted in a discovery of a nonpathogenic <em>R. vitis</em> strain ARK-1. By soaking grapevine roots with a cell suspension of strain ARK-1 prior to planting in the field, ARK-1 treatment significantly reduced the number of plants with crown gall symptoms. Several field trials results indicated that ARK-1 was very useful in the fields, not only for grapevine but also for diverse plant species. In experiments where a mixture of ARK-1 and the tumorigenic strain at a 1:1 cell ratio was examined <em>in vitro</em> and <em>in</em><em> planta</em>, expressions of the virulence genes <em>virD2</em> and <em>virE2</em> of tumorigenic strain were significantly lower. The suppression of virulence genes, which can result in a reduction of gall formation and the pathogen population, seems to be a unique mechanism of ARK-1. These results indicate that ARK-1 is a promising new agent to control grapevine crown gall.</div>