Department of Life Science, Fu Jen Catholic University, HsinChuang 24205, Taipei, Taiwan, Republic of China
TaiChung District Agricultural Research and Extension Station, Council of Agriculture, Executive Yuan, Taiwan, Republic of China
Leaf blight symptoms on coriander (Coriandrum sativum) were observed during the summers of 2000 to 2002 in fields at the Beidou and Sijhou townships, Changhua County, Taiwan. Symptoms first appeared as small spots on the lower sides of leaves and stems. The centers of the spots quickly turned brown and were surrounded by whitish yellow halos. The brown spots and halos enlarged rapidly and coalesced into irregular, yellowish or brownish dry dead areas on the leaf. V-shaped and chlorotic blotch symptoms were also found at the margins of leaves. Isolations from diseased leaves consistently yielded bacterial colonies that were yellow and glistening on nutrient and potato dextrose agar media. Five representative strains were chosen for further characterization. All strains were gram-negative rods, aerobic, and produced yellow, nonwater soluble, xanthomonadin pigments identified by thin-layer chromatography (1). The strains were positive for catalase and β-galactosidase and negative for oxidase, nitrate reductase, urease, and tryptophanase (indole production) and hydrolyzed starch, gelatin, and esculin. Hydrogen sulfide was produced from cysteine. L-asparagine was not sufficient as a sole carbon source for growth. In Dye's medium C, acids were produced from metabolizing arabinose, glucose, and sucrose but not from rhamnose, cellobiose, lactose, dulcitol, mannitol, and sorbitol. The bacterium was identified as Xanthomonas campestris. Almost complete 16S rDNA sequence of strain TC3 (1,502 bp; GenBank Accession No. AY604178) was determined and compared with available 16S rDNA sequences in GenBank. The sequence was highly identical (99%) to those of Xanthomonas campestris pathovars. Coriander plants were inoculated by spraying bacterial suspensions (108 CFU/ml) on leaves, enclosed in a plastic bag to maintain high humidity for 2 days, and kept in a growth chamber at 28°C. Typical symptoms were observed in 2 to 6 days in all four inoculated plants and appeared to be identical to those observed in the fields. Control plants were inoculated with sterile distilled water and showed no symptoms. The bacterium was readily reisolated from diseased leaves. Bacterial leaf blight of coriander was first reported in India, and the pathogen was identified as X. campestris pv. coriandri (2). To our knowledge, this is the first occurrence of this bacterium on coriander in Taiwan.
References: (1) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001. (2) M. C. Srinivasan et al. Proc. Indian Acad. Sci. Sect. B 53:298, 1961.