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First Report of Stem Spots Caused by Alternaria sp. on Berberis sp. in Iran

During the summer of 2004, approximately 150 Berberis sp. (Berberis thunbergii cv. Rose Glow) showing dark brown, eye-like elongated spots (7 to 22 mm long and 1 to 3 mm wide) on stems near the crown toward the top were observed in a park in Tehran, the capital of Iran. Red and yellow spots on the leaves and defoliation were also recorded for some of the affected plants. A total of 28 samples from 16 individual plants (sampling included all symptomatic parts of the plants) were collected and evaluated for the possible casual agent of the disease. Fungi with spores that are characteristic of the genus Alternaria (2), including dark mycelium and brief and simple conidiophores with catenulate dictyospores, were isolated from the detached leaf and stem pieces of diseased plants. The pathogenicity of five isolates was investigated using Koch's postulate. Twenty cut stems and 10 rooted plants of Berberis sp., with or without wounding on their stems and leaves, were inoculated with the spore suspension (10⁴ spores per ml) prepared by using 10-day-old cultures of the isolates grown on potato dextrose agar at 25°C in the dark. The inoculated cut stems were covered for 3 days with a plastic tent and kept in a greenhouse at 25 ± 5°C with more than 12 h of light. These covers were not used for the rooted plants that were inoculated under field conditions. For each test, at least two controls were used. Symptoms similar to those observed in the field appeared on inoculated stems in 6 to 7 days. On leaves, dark, reddish brown spots (different from the field observations) were induced 3 to 4 days after inoculation. The disease on leaves, which eventually led to defoliation, was more severe than that observed in the field. Stem spots occurred on covered and uncovered inoculated plants; however, the lesions on the covered plants were deeper than those on the uncovered plants. Both types of plants died 3 to 4 weeks after inoculation. Although the fungi were isolated from diseased plants from one park, similar symptoms also were observed on Berberis sp. planted in other parks and streets, etc. The genus Alternaria (Deuteromycetes) caused leaf and stem spot diseases on different plant hosts (1). To our knowledge, this is the first report of a natural occurrence of Alternaria sp. on Berberis sp. in Iran.

References: (1) G. N. Agrios. Plant Pathology, 4th ed., Academic Press, NY, 1997. (2) M. B. Ellis. More Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, 1976.