Bacterial leaf spot of leafy crucifers in Oklahoma caused by Pseudomonas syringae pv. maculicola

During 1995 and 1996, bacterial leaf spots severely damaged fields of kale, spinach mustard, and turnip in Oklahoma. Symptoms were small, brown, necro tic spots with irregular edges surrounded by chlorotic halos. Lesion margin s were often water-soaked on the abaxial surface. The spots enlarged and co alesced, causing extensive leaf yellowing and necrosis. Nineteen strains of a fluorescent Pseudomonas spp, were isolated from symptomatic plants. LOPA T tests and carbon source oxidation using Biolog GN MicroPlates were used t o classify the strains as I! syringae. Cluster analysis of carbon source ox idation profiles for the local strains and selected reference strains of P. syringae pv. maculicola and pv. tomato produced one group with 79.5% simil arity. In spray inoculations, all local strains caused chlorotic or water-s oaked lesions on collards, kale, cauliflower, and tomato. A few local strai ns caused necrotic lesions on mustard. Most local strains caused one of the three lesion types on turnip and spinach mustard. Reference strains of P. syringae pv. maculicola caused similar symptoms. All but three of the local strains produced coronatine in vitro. The local strains were thus classifi ed as P. syringae pv. maculicola, the cause of bacterial leaf spot of cruci fers. Two distinct groups of I! syringae pv. maculicola were identified by repetitive sequence-based polymerase chain reaction (rep-PCR) with both REP and BOXA1R primers. Three subgroups within each group were further identif ied using the BOXAIR primer. Except for two strains of P. syringae pv, toma to which were pathogenic on crucifers, the pathovars maculicola and tomato had different genetic fingerprints. The pathogen was recovered from seven o f ten fields sampled during 1994 to 1996. In five of the fields with P. syr ingae pv. maculicola, pathovars of Xanthomonas campestris were also isolate d from lesions forming a bacterial disease complex. This is the first repor t of bacterial leaf spot caused by P. syringae pv. maculicola on leafy cruc ifers in Oklahoma.