A New Disease, Arboricola Leaf Spot of Bell Pepper, Caused by Xanthomonas arboricola.
In June 2007, a leaf spot disease was observed on seedlings of bell pepper (Capsicum annuum L. var. angulosum) in a commercial greenhouse in Iksan City, Korea. Symptoms on leaves included small, irregularly shaped, brown lesions with yellow halos and marginal necrosis. Four bacterial isolates, BC2526, BC2527, BC2528, and BC2529, were obtained from the diseased plants. The isolates were gram-negative aerobic rods with a single flagellum. On peptone sucrose agar, colonies were yellow and raised with smooth margins. Pathogenicity was confirmed by spraying cell suspensions containing 106 CFU/ml onto seedlings of bell pepper (cv. Fieste), tomato (Solanum lycopersicon cv. Seokwang), and hot pepper (Capsicum annuum cv. Daekwang) in a greenhouse maintained at 26 ± 3°C. The isolates induced symptoms, spots, and margin blights on leaves of bell pepper, tomato, and hot pepper 2 weeks after inoculation. No symptoms were noted on the control plants inoculated with sterilized distilled water. The identity of the bacteria was confirmed with the Biolog Microbial Identification System, version 4.2 (Biolog Inc., Hayward, CA). The gyrB region was partially sequenced to aid in identification of four isolates using PCR primers reported by Parkinson et al. (1). A 701-bp fragment of the gyrB region from the isolates was compared with sequences of the reference strains of Xanthomonas available in the DDBL/EMBL/GenBank databases (4). The bacterial isolates clustered with Xanthomonas arboricola pathovars in a phylogenetic tree generated with the neighbor-joining method in MEGA (version 4.1) (3). The sequence of the gyrB from the isolates had distance indexes of 0.016, 0.014, 0.016, 0.013, 0.037, and 0.019 as determined by the Jukes-Cantor model (2) with sequences of the reference strains of X. arboricola pvs. pruni (EU498953), celebensis (EU498984), corylina (EU499002), juglandis (EU 498951), populi (EU 499035), and a X. arboricola strain from bell pepper (EU 499039) (4), respectively. To our knowledge, this is the first report of a leaf disease on bell pepper caused by X. arboricola. We propose the name arboricola leaf spot for the disease. Further studies are required for determining pathovar status of the strain. Nucleotide sequence data reported are available under Accession Nos. GQ502678, GQ502679, GQ502680, and GQ502681 for gyrB of BC2626, BC2527, BC2528, and BC2923, respectively. The disease is expected to have a significant economic impact on tomato and pepper production in Korea. References: (1) N. Parkinson et al. Int. J. Syst. Evol. Microbiol. 59:264, 2009. (2) N. Saitou and M. Nei. Mol. Biol. Evol. 4:406, 1987. (3) K. Tamura et al. Mol. Biol. Evol. 24:1596, 2007. (4) J. M. Young et al. Syst. Appl. Microbiol. 31:366, 2008.