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First Report of Bacterial Blight of Geranium Caused by Xanlhomonas campestris pv. pelargonii in Argentina. G. Dal Bello, Facultad de Ciencias Agrarias y Forestales - UNLP y CIC. Prov. de Buenos Aires. CC 31 (1900) La Plata, Argentina . M. Carranza, Facultad de Ciencias Agrarias y Forestales - UNLP y CIC. Prov. de Buenos Aires. CC 31 (1900) La Plata, Argentina. Plant Dis. 79:103 . Accepted for publication 25 October 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-80-0103A.

In the summer arid fall of 1994, nearly 70% of geranium plants (Pelargonium x hortorum L. H. Bailey) collected from gardens in La Plata, Argentina, had foliage with symptoms of bacterial blight. Chlorotic, V-shaped lesions formed from the margins of the leaf blade, dark veins appeared in infected tissues, and older lesions were dried and dark brown. Dead leaves abscised, leaving petioles attached to the stem. To determine the causal organism, tissues from recently abscised leaves were ground in sterile water, and the macerate was plated onto sucrose-peptone agar (SPA) (1), then incubated at 25°C. Yellow, mucoid, gram-negative bacteria were isolated and 12 axenic cultures were identified as Xanlhomonas campestris pv. pelargonii on the basis of physiological characteristics (positive for aesculin hydrolysis, growth at 350C, acid production from arabinose, glucose, and mannose, and negative for urease production) and growth on semiselective media (positive on BSCAA, XCS, and Tween, and negative on SX) (as found in Schaad and Stall’s laboratory guide). Pathogenicity was confirmed on 5-month-old plants of zonal (P. hortorum) and ivy-leaf (P. peltatum (L.) L’Her. ex Ai-ton) geraniums that were sprayed with bacterial suspensions containing 108 CFU/ml in saline (0.85% NaCl), covered with plastic bags for 48 h, and grown at 25°C in a greenhouse. Symptoms typical of those found on garden plants were evident within 2 weeks. Symptoms were more apparent on the zonal than on the ivy-leaf geraniums. The pathogen was reisolated on SPA and recharacterized as X. c. pv. pelargonii by the physiological tests. This is the first report of bacterial blight of geranium in Argentina.

Reference: (1) A. C. Hayward. Nature 186:405, 1960.