First Report of Bacterial Leaf and Flower Spot of Zinnia in Louisiana. G. E. Holcomb, Department of Plant Pathology and Crop Physiology, Agricultural Experiment Station, and Cooperative Extension Service, Louisiana State University, Baton Rouge 70803. C. Hollier, and H. K. Whitam, Department of Plant Pathology and Crop Physiology, Agricultural Experiment Station, and Cooperative Extension Service, Louisiana State University, Baton Rouge 70803. Plant Dis. 69:360. Accepted for publication 9 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-360b.
A severe leaf and flower spot of Zinnia elegans Jacq. was observed in Louisiana State University variety trial plantings and in seedlings sent to the university’s Plant Disease Clinic from a commercial grower. Test plot losses were 80–100% in highly susceptible varieties. Plants of cv. Small World Cherry were infected but not killed, and losses in cvs. Peter Pan Princess and Peter Pan Bold were near 50%. July plantings of these three cultivars were nearly disease-free when observed in September. A yellow-pigmented, gram-negative, strictly aerobic bacterium repeatedly isolated from leaf and flower spots was identified as Xanthomonas campestris pv. zinniae (Hopkins & Dowson) Dye. This bacterium produced leaf spots with chlorotic halos within 10 days after healthy zinnia plants were misted with bacterial suspensions. The pathogen was reported in the United States first from Ohio in 1972 and later from North Carolina and Florida.