Forest Pathology Laboratory, Forestry and Forest Products Research Institute Kyushu Research Center, 4-11-16, Kurokami, Kumamoto, 860 Japan

Background and objectives
Japanese evergreen oaks (Quercus spp.) are distributed from the center to the southwest of Japan. Some of them are extensively cultivated for planting in parks or along roadsides. About ten years ago, dieback occurred in the nurseries of evergreen oaks in Kagoshima and Miyazaki prefectures. Our primary study [1] suggested that the dieback on Q. myrsinaefoliawas a bacterial disease caused by a xanthomonad. In recent years, similar diseases occurred on other Japanese oaks (including deciduous oaks) in the nurseries and extended to artificial and natural forests. In this presentation, we show the taxonomic study about the causal bacteria of these diebacks occurring onQ. myrsinaefoliaand other Japanese oaks.

Materials and methods
Oak bacteria were isolated from affected shoots or twigs of oaks collected in the nurseries and the forests of Kyushu district of Japan during the period from 1995 to 1997. Inoculation experiments were made by puncturing young shoots with a needle through bacterial suspension (109 cfu/ml) spread over the surface. Bacteriological characteristics were investigated by the protocol described by Schaad [2] and others. Host ranges were investigated by inoculation experiments to various plants with the standard strains isolated from each oak.

Results and conclusions
The symptoms are shoot blight resulting in dieback. Brown to black necrotic lesions occur on young shoots or petioles and develops to kill the shoot, twig and occasionally young stem. If the lesion stops developing, a crack occurs and becomes a canker. At the beginning of the disease, unclear discoloration or yellowish bacterial ooze often appears on the young shoot. The disease mainly occurs from rainy season to autumn (June to October), and especially increases in summer. The bacteria, forming yellowish, muddy and uniform colony, were primary and mainly isolated from affected shoots and twigs of Q. acutissima,Q. aliena,Q. gilva,Q. glauca,Q. myrsinaefolia,Q. hondae,Q. phillyraeoides,Q. salicina,Q. serrata,Q. sessilifolia. By inoculation experiments, it was ascertained that these bacteria possessed pathogenicity to their original host oaks and each standard strain isolated from the ten species of oaks had similar and wide host ranges on Japanese oak trees. On the basis of their bacteriological characteristics and those of xanthomonads described in Bergey's Manual (9th Ed.), causal bacteria were identified as Xanthomonas campestris Dowson 1939. In the Approved List, CAB index and others sources there is no available named xanthomonad which affects Quercus spp. From the symptoms, we propose to name the disease 'Bacterial shoot blight'.

1. Ishihara M, Kawabe Y, Akiba M, 1996. Ann. Phytopathol. Soc. Jpn. 62:304.
2. Schaad NW,1988. Laboratory Guide for Identification of Plant Pathogenic Bacteria 2nd Edition, APS PRESS, pp.1-164.