A new bacterial disease observed onQuercus myrsinifolia

Abstract

This is the first report of a new bacterial disease occurring on Quercus myrsinifolia in the nurseries of the Kyushu district in Japan. The main symptoms are shoot and twig blight, which begins with black necrotic lesions. In addition, unclear blackish discolorations, bacterial ooze and water-soaked lesions were observed as early symptoms, and spindle-shaped cankers and stem cankers with irregular surface were observed as secondary symptoms. The blight symptoms observed on the current-year shoots were first observed during the rainy season and continued until autumn (June–October). In summer, the symptoms were pronounced. A yellowish bacterium was consistently isolated from the affected shoots of Q. myrsinifolia, and on inoculation into healthy trees, it caused the same symptoms, which were more severe after wound inoculation than after non-wound inoculation. Wound inoculation also caused the disease symptoms on Quercus spp., Fagus crenata and Lithocarpus glaber, but not on several other species of Fagaceae. The causal bacterium was identified as Xanthomonas arboricola based on its morphological, cultural and biochemical characteristics and genetic sequence analysis of 16S rDNA, 16S-23S spacer regions and gyrB. To our knowledge, there are no previous records of xanthomonads causing shoot blight on fagaceous plants like Q. myrsinifolia. Therefore, we postulate that the shoot blight of Q. myrsinifolia is a new bacterial disease. We propose the name of the disease to be ‘bacterial shoot blight’ based on its main symptoms.