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Investigation in the occurrence of leaf spot diseases on sissoo (Dalbergia sissoo) caused by Alternaria alternata were conducted in various forest nurseries of Navsari district in Gujarat. The maximum percent disease incidence (52.50%) was observed at Vansda forest nursery. Microscopic examination and tissue isolation from leaves of infected seedlings of Dalbergia sissoo collected from those of different forest nurseries yielded culture of Alternaria alternata. Most of the plants were found infected by showing varying degree of infection indicating their susceptibility to the pathogen at almost all stages of seedling growth. Infection spots were dark brown; varied in size and shape and coalesced to form larger spots. The fungus sporualted on the lower surface of the leaves. Microscopic examination revealed the presence of micro and macro conidia of Alternaria alternata with brwon mycelium. The pathogenicity tests were carried out by inoculation method and mycelium/spore spray method. Both the methods successfully produced typical leaf spot symptoms similar to those observed under natural conditions as described in literature, confirming pathogenic nature of the fungus. Among the two techniques, inoculation method was found to be the quickest and most effective method for proving the pathogenicity of Dalbergia sissoo. Thus, the causal agent of the Dalbergia sissoo leaf spot was identified and confirmed as Alternaria alternata.
Fungal diseases, leaf spot, Dalbergia sissoo, Alternaria alternata
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