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Disease Note.

First Report of Crucifcr Bacterial Leaf Spot Caused by Pseudomonas syringae pv. maculicola in Argentina. A. M. Alippi, Laboratorio de Fitopatologfa, Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Calles 60 y 119, c.c. 31, 1900 La Plata, Argentina. L. Ronco, Laboratorio de Fitopatologfa, Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Calles 60 y 119, c.c. 31, 1900 La Plata, Argentina. Plant Dis. 80:223. Accepted for publication 6 December 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0223B.

In April 1995 (austral autumn), typical bacterial spot symptoms were observed on brussels sprouts leaves (Brassica oleracea L. var. gemmifera DC. cv. Oliver ) in a commercial field in La Plata, Argentina. Affected plants had small brown spots with irregular edges surrounded by chlorotic haloes. The spots were approximately 1 mm in diameter and covered most of the leaf surface. The spots enlarged and coalesced, forming large necrotic areas limited by the main veins. In some plants, leaves appeared deformed and broken, giving a ragged appearence. Disease incidence approached 100%. No pathogenic fungi were associated with symptomatic plants. Bacteria consistently isolated from lesions formed white, glistening, convex colonies on sucrose peptone agar (SPA) and a water-soluble, green fluorescent pigment on King's medium B. Bacteria were aerobic, gram-negative, non-spore-forming rods, averaging 0.67 x 2.18 µrn. In levan-oxidase-potato rot-arginine dihydrolase-tobacco hypersensitivity (LOPAT) tests, all eight strains induced a hypersensitive response in tobacco plants, did not cause soft rot of potato tubers, and were positive for levan and negative for oxidase and arginine dihydrolase. Acid was produced aerobically from sucrose and d-mannitol but not from d-(+)salicin, d-(-)arabinose, or sorbitol. Variable results were obtained with inositol. The strains did not hydrolyze starch and exhibited an oxi-dative metabolism of glucose. Colonies developed at 30C but not at 41?C. Strains were positive for catalase and indole production. They did not utilize Tween 80 nor reduce nitrates to nitrites. Coronatine production was determined using Escherichia coli (ATCC 25922) as indicator strain added to Pseudomonas minimal medium (PMS) agar at 107 CFU/ml (2). Zones of growth inhibition were observed around all the cultures tested. Pathogenicity was verified on greenhouse-grown broccoli (Brassica oleracea L. var. italica cv. Atlantic), cauliflower (B. oleracea var. botrytis cv. Snow March), brussels sprouts cv. Oliver and tomato (Lycopersicon esculentum Mill hybrid LSL TT-6) by both spray and infiltration inoculation with bacterial suspensions (109 and 106 CFU/ml, respectively) (I). Symptoms on inoculated brussels sprouts were identical to those observed on brussels sprouts in the field, and bacteria recovered from in fected leaves had physiological characteristics identical to those used as inoculum. The microorganism was identified as Pseudomonas syringae pv. maculicola (1,2). The disease is also known as pepper or peppery leaf spot. This is the first report of bacterial leaf spot of crucifers in Argentina.

References: (1) M. Hendson et al. J. Appl. Bact. 73: 455, 1992. (2) W. L. Wiebe and R. N. Campbell. Plant Dis. 77: 414, 1993.