Stem Canker and Leaf Spot of Poinsettia Caused by Pseudomonas viridiflava in Florida. Arthur W. Engelhard, Gulf Coast Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, Bradenton 34203. J. B. Jones, Gulf Coast Research and Education Center, University of Florida, Institute of Food and Agricultural Sciences, Bradenton 34203. Plant Dis. 74:528-529. Accepted for publication 26 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0528.

Stem cankers developed on outdoor poinsettia (Euphorbia pulcherrima) grown near Bradenton, FL, in December 1984. A fluorescent bacterium was isolated from the cankers. The bacterium was positive for tobacco hypersensitivity, grew on a minimal medium containing dl-lactate, d(?)-tartrate, or erythritol but not sucrose, and produced a negative reaction for arginine dihydrolase and oxidase and a positive reaction for potato soft rot and levan. The pathogen was identified as Pseudomonas viridiflava. It produced stem cankers on all seven cultivars of poinsettia inoculated on the stems and leaf spots on the two cultivars inoculated on the leaves. The disease was most severe on stems at 10 and 16 C; it was mild at 27 C and absent at 32 C.