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First Report of Bacterial Blight Caused by Pseudomonas viridiflava on Pea in Spain

Because production of dry peas (Pisum sativum L.) is increasing in Spain, disease surveys were carried out from 2004 to 2006 in Castilla y Leon, the largest pea-producing region. In May of 2004, a leaf and stem blight caused an estimated 25% loss in yield in pea (cv. Messire) fields in El Cerrato (Palencia). Bacteria were isolated on King's B medium from 10 symptomatic plants from different fields (3). Thirty gram-negative isolates produced fluorescent, yellowish mucoid colonies. All isolates showed oxidative glucose metabolism on Hugh-Leifson medium and were levan and oxidase negative, potato soft rot positive, arginine dihydrolase negative, and tobacco hypersensitive positive. They also hydrolyzed esculine and gelatine. These results were different than those expected by Pseudomonas syringae pv. pisi and P. syringae pv. syringae (3). API 50 CH tests (bioMerieux, Marcy l'Etoile, France) revealed that all the isolates used the following carbon sources: glycerol, erythritol, l-arabinose, ribose, d-xylose, galactose, d-glucose, d-fructose, d-manose, inositol, manitol, sorbitol, d-raffinose, d-fucose, and d-arabitol. This nutritional profile is identical with that of P. viridiflava strain CFBP 6730, originally from pea plants in France. Therefore, these isolates were tentatively identified as P. viridiflava (2). Since a preliminary test demonstrated that 9 of the 30 isolates were pathogenic on pea plants, pathogenic isolates P44, P45, and P46 were selected arbitrarily for further tests. These three isolates plus strains HRI-W 1704 (P. syringae pv. pisi type race 6) and CFBP 1769 (P. syringae pv. syringae) were inoculated onto 10 pea seedlings (cv. Messire) each in two identical trials, following a described protocol (1). Seedlings inoculated with sterile distilled water were used as controls. After 10 days of incubation in a growth chamber at 22°C and 80% relative humidity, severe rotting and collapse similar to symptoms observed in fields appeared on pea seedlings inoculated with isolates P44, P45, and P46, while water-soaked leaf spots and necrotic symptoms were caused by P. syringae pv. pisi and P. pv. syringae. No symptoms were observed on plants inoculated with sterile water. Isolates recovered from symptomatic stems showed the same morphological and biochemical features of the original isolates. Sequences of 1,399 bp long from the three isolates (GenBank Accession Nos. GQ398128, GQ398129, and GQ398130) were 100% identical to P. viridiflava 16S rDNA database reference sequences. To our knowledge, this is the first report of P. viridiflava causing a disease of pea in Spain. The disease has been reported in New Zealand (4) and France (2).

References: (1) E. M. Elvira-Recuenco et al. Eur. J. Plant Pathol. 109:555, 2003. (2) C. Grondeau et al. Plant Pathol. 41:495, 1992 (3) N. W. Schaad et al., eds. Laboratory Guide for the Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001. (4) J. D. Taylor et al. N. Z. J. Agric. Res. 5:432, 1972.