Disease Note.

Leaf Spot and Stem Canker of Ginkgo biloba Caused by Pseudomonas syringae. A. L. Bishop, California Department of Food and Agriculture, 1220 N Street, P.O. Box 942871, Sacramento 94271-0001. L. Basarich, California Department of Food and Agriculture, 1220 N Street, P.O. Box 942871, Sacramento 94271-0001. Plant Dis. 73:368. Accepted for publication 17 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0368C.

Homogeneous cultures of Pseudomonas syringae van Hall were consistently isolated from leaf spots and stem cankers on potted Ginkgo biloba L. grown under sprinkler irrigation in a nursery in Sacramento County, California. Sunken black cankers girdled stems up to I cm in diameter, causing death of distal parts. Leaf spots were either round, 2-5 mm in diameter, with necrotic centers and bright yellow chlorotic margins, or elongated and delimited by veins, with chlorotic margins forming streaks extending to the margins of leaves. Necrotic centers dropped out of foliar lesions in some cases, causing shot holes or tattering. Disease incidence approached 100% in affected plantings and was distributed through several plantings of various ages. Inoculation by pinprick of potted Ginkgo saplings (approximately 2 yr old) with strains isolated from either leaf spots or stem cankers reproduced both types of lesion in the greenhouse (1-2 wk for leaf spots, about 1 mo for cankers). The pathogen was readily recovered from lesions on inoculated plants. The pathovar involved is as yet undetermined, but results of carbon source utilization tests and bean pod bioassays with strains from Ginkgo are typical of P. s. pv. syringae. This is the first report of a bacterial disease of Ginkgo.