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First Report of Leaf Spot of Dracaena reflexa Caused by Burkholderia gladioli Worldwide

In December 2008 (austral summer), a new disease of Dracaena reflexa Lam. cv. Anita was observed in a postentry quarantine greenhouse near Auckland, New Zealand on plants imported from Costa Rica. Symptoms included rust-colored, water-soaked lesions with chlorotic margins approximately 5 by 10 mm. When the disease was first noticed, incidence approached 80%, but subsequent reduction in greenhouse temperature dramatically reduced symptom expression and lesions were only visible on some leaf tips. Bacteria consistently isolated from the lesions on King's medium B (KB) were cream-colored, shiny, and produced a yellow, diffusible, nonfluorescent pigment. All isolates were able to rot onion slices. On the basis of BIOLOG (Hayward, CA) carbon utilization profiles, isolates were initially identified as Burkholderia gladioli (Severini 1913) Yabuuchi et al. 1993 with a probability index of 100% and a similarity index of 0.85. For molecular identification, a near full-length sequence of the 16S rDNA gene was amplified from all isolates using primers fD2 and rP1 (1), obtaining a PCR product of approximately 1,500 bp. The nucleotide sequences were 100% identical to a number of B. gladioli GenBank entries, including Accession Nos. EF193645 and EF088209. To confirm pathogenicity, three isolates (two isolated prior to greenhouse temperature reduction and one after) were used. Three D. reflexa plants were inoculated per bacterial isolate by wounding three young fully expanded leaves on each plant (four wounds per leaf) and spraying the leaves with a bacterial suspension in sterile distilled water at 10⁸ CFU/ml. At the same time, Gladiolus nanus plants were inoculated in a similar manner. Control plants (D. reflexa and G. nanus) were wounded and sprayed with sterile distilled water. All inoculated plants were covered with plastic bags to maintain humidity and placed in a growth chamber at 25°C. At 3 days, all inoculated plants began to show water soaking and reddish coloration around the inoculation sites, and by 7 days, the lesions had expanded to resemble natural infection. Bacteria isolated on KB from the leading edge of each lesion were morphologically identical to the initial isolates. No bacteria were recovered from the wound sites on the control plants. The 16S rDNA sequences of selected isolates from inoculated plants showed 100% identity to the sequences of the initial isolates, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of B. gladioli causing leaf spot of D. reflexa in the world.

Reference: (1) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991.