| Summary: | This study was carried out to investigate the pathogenicity of Alternaria alternata and the effect of its metabolites on L. japonica from 2015- 2016 in Birjand plain area in eastern Iran. A. alternata isolates were inoculated on L. japonica detached leaves in laboratory conditions, on plants by spore suspension in the greenhouse and on young branches by fungal mycelia. The effect of A. alternata metabolites was examined by injection of extracted metabolites from a 10-day culture of the fungus in a Czapek broth media into the leaves of the plant. Inoculated detached leaves, after 3 to 7 days of inoculation, exhibited different ranges of chlorosis and necrosis, with or without a yellow halo around some of this spot. Leaves of inoculated plants in the greenhouse showed chlorosis, necrosis and leaf spots with (Mo8) or without (H44) a yellow halo. Inoculated stems demonstrated rotting and death in the inoculation site and wilting of stems. Metabolites of some isolates particularly isolate with a yellow halo (Mo8) in inoculated detached leaves, caused necrotic leaf tissues five days after injection. The results showed that A. alternata could be a cause of leaf spot, chlorosis, and necrosis, and the metabolites of some isolates can cause the death of leaf cells of L. japonica. This is the first report of the A. alternata pathogenicity on this plant in the eastern part of Iran.
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