“Investigations on Alternaria alternata Causing Blight Disease in Tomato (Solanum lycopersicum L.)”

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Among the several diseases of tomato, leaf blight disease caused by Alternaria alternata is one of the most destructive disease which causes heavy losses in fruit yield of tomato. Per cent disease index (PDI) varied from 34.34 to 49.98 per cent in four surveyed districts viz., Kota, Bundi, Baran and Jhalawar of Hadoti region of Rajasthan. Maximum PDI was recorded in Charchoma village of Kota district (49.98%) while minimum was recorded in Azampur village of Jhalawar district (34.34%). Among the districts, disease severity was found to be maximum in Kota (44.06%), while least in Jhalawar (38.08%). The Pathogen was isolated from infected tomato plants showing typical leaf blight symptoms, purified and its pathogenicity was proved. The pathogen produced dark brown to black colony with septate mycelium and acropetal chain of ellipsoidal brown or muriform conidia, thus identified as Alternaria alternata which was further got confirmed by ITCC, Division of Plant Pathology, IARI, New Delhi (Ref. ID 11, 291.20). Cultural and morphological variability regarding colony diameter, colony colour, growth pattern, margin colour, topography, thickness of mycelium mat and sporulation were observed among seven isolates of Alternaria spp., collected during survey. AltKo1 isolate from Charchoma village of Kota showed maximum growth and sporulation on Potato dextrose agar (PDA) medium. Among seven solid culture media, PDA medium found better for mycelium growth and sporulation of Alternaria alternata. Out of seven liquid media, Oat meal broth gave maximum dry mycelium weight followed by Potato dextrose broth. Among seven fungicides tested, Hexaconazole @ 5 EC recorded maximum inhibition of mycelial growth (with mean 97.96%) at all concentrations under in vitro condition. Out of four bio-agents tested, Trichoderma harzianum found most effective followed by Trichoderma viride under in vitro condition. Out of six botanical extracts tested in vitro, Azadirachta indica (leaf extract) gave best result with 96.11 per cent inhibition of mycelial growth followed by seed extract of Azadirachta indica (94.11%).
“Investigations on Alternaria alternata Causing Blight Disease in Tomato (Solanum lycopersicum L.)”