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First Report of Leaf Spot and Blight of Strelitzia reginae Caused by Burkholderia gladioli in Italy

During the summer of 2005, a new disease of bird of paradise (Strelitzia reginae Aiton) was observed on young seedlings (2 to 3 months old) in a nursery located in Giarre (Catania) in eastern Sicily. Symptoms included brown, water-soaked leaf spots that first appeared after seedling emergence and then gradually enlarged and became necrotic. Occasionally, during wet conditions, seedlings were completely blighted, resulting in total loss. The disease was observed on 10% of the 3,000 plants present in one nursery. A single bacterial colony was consistently isolated on King's medium B (KB) supplemented with 0.01% cycloeximide from surface-sterilized, brownish lesions and water-soaked leaf tissues. The isolates were purified on nutrient agar (NA). Three bacterial strains isolated from three different symptomatic plants were used for pathogenicity and identification tests on S. reginae plants. Five plants were inoculated per bacterial strain by spraying the leaves with a buffer phosphate suspension (0.1 M) at 10⁶ CFU/ml prepared from KB plates incubated for 24 h at 28°C and wounding the leaves (four wounds per leaf) with a sterile needle. The same number of noninoculated plants was used as control. All plants were covered with plastic bags and maintained in a greenhouse at 25 ± 1°C with 95 to 100% relative humidity until symptoms occurred 3 to 4 days later. All three bacterial strains tested were virulent and caused symptoms identical to those observed in the nursery. No symptoms were observed in control plants. Koch's postulates were fulfilled by the reisolation of the three strains from inoculated plants. The strains were gram-negative, aerobic rods, grew aerobically, were white and nonmucoid on yeast dextrose calcium carbonate agar, nonfluorescent on KB, produced diffusible nonfluorescent pigment on KB, and were oxidase and urease negative. All strains utilized glucose, arabinose, mannose, mannitol, N-acetylglucosamine, gluconate, caprate, malate, citrate, and phenyl acetate and none of the strains produced indole or acidified glucose. Using the API 20NE test strips (bioMérieux, Marcy l'Etoile, France) incubated at 28°C for 24 to 48 h, all strains were initially identified as Burkholderia cepacia. On the basis of the nutrient profiles revealed by the BIOLOG system (Microlog System Release 4.2, Hayward, CA), the strains were identified as B. gladioli (Severini 1913) Yabuuchi et al. 1993. The index of probability was 100% and the index of similarity was 0.75%. For molecular identification of strains, 16S rDNA was amplified by using species-specific primers Eub-16-1 and Gl-16-2₄₅₇, obtaining a polymerase chain reaction (PCR) product of 463 bp (1). PCR analysis indicated that the strains belong to B. gladioli. Other bacteria have been previously reported in Italy as pathogens of Strelitzia spp. (2,3). To our knowledge, this is the first outbreak of leaf spot and blight caused by B. gladioli on S. reginae.

References: (1) A. Bauernfeind et al. J. Clin. Microbiol. 37:1335, 1999. (2) P. Bella et al. J. Plant Pathol. 82:159, 2000; (3) G. Polizzi et al. Plant Dis. 89:1010, 2005.