Abstract
A new bacterial disease was found on leaves, berries and their pedicels of grapevine (Vitis vinifera cvs. Kaiji, Rosario Bianco and others) in orchards of Koshu and Minami-Alps cities, Yamanashi Prefecture, Japan in 2008 and 2009. Leaf spots were restricted by veins, angular, water-soaked, first yellowish white to yellow, and later turned brown to blackish brown, and necrotic. Oval, slightly depressed, brown to blackish brown, necrotic spots formed on young berries and pedicels. The causal bacterium, which was demonstrated by inoculation and reisolation to be pathogenic on grapevine, was a gram-negative, aerobic rod with one polar flagellum. It formed yellow slimy colonies and had biochemical and physiological characters similar to those of Xanthomonas species. Phylogenetic analysis based on 16S rRNA gene sequences showed that it belonged to the Xanthomonas campestris core of the Xanthomonas clade. gyrB phylogeny and rep-PCR analysis further clarified that it formed a distinct clade with X. arboricola pathovars, in which the analyzed grapevine isolates were interspersed with X. arboricola pathovars. On the basis of the phenotypes and genotypes, we identified the causal bacterium as Xanthomonas arboricola Vauterin, Hoste, Kersters and Swings 1995. This report is the first in the world of a grapevine disease caused by X. arboricola, so we propose the name bacterial spot of grapevine for the disease. The results of grapevine inoculation tests, gyrB phylogenic analysis, rep-PCR analysis, and disease surveys in Yamanashi Prefecture showed that the causal bacterium was a genetically heterogeneous complex of opportunistic pathogens with weak pathogenicity.
