Plant Pathology

Early blight is the most common and devastating disease of potato (Solanum tuberosum L.) caused by Alternaria solani (Ellis & Martin) Jones and Grout. In vitro experiments were conducted during 2017-2018 to search appropriate growth medium of A. solani, as well as suitable fungi toxicant through quick screening methods. Seven different growth medium were used to culture the fungus in laboratory. Mycelial growth was very fast in Potato Dextrose Agar (PDA) followed by Richards’s Agar (RA) medium. Intermediate growth habit was recorded in Sabouraud’s Agar (SA), Czapek’s Dox Agar (CDA) and Potato Carrot Extract Agar (PCEA). The growth was very slow in Oat Meal Agar (OMA) and Malt Extract Agar (MES) at 72 hours of incubation. On bioefficacy evaluation, Infield Ayur showed very negligible effect to restrict mycelial growth and conidia formation, whereas Indofil M-45 (mancozeb) was more efficacious followed by Indofil Z-78 (zineb), Merger (tricyclazole + mancozeb) and Ishaan (chlorothaloni...

Early blight caused by Alternaria solani (Ellis and Martin) Jones and Grout is one of the most serious diseases of potato throughout the world including India. Field experiments were conducted during Rabi season, 2016-17 and 2017-18 at Benuria, Bolpur under Red and Lateritic Agro-climatic zone of West Bengal for developing suitable management practice against early blight of potato (cv. Kufri Jyoti). Necessary laboratory studies were done in the Department of Plant Protection, Palli-Siksha Bhavana, Visva-Bharati. Symptoms of the disease appeared mainly on leaves, petioles and stems, and in severe condition on tubers. Initially the symptoms observed on lower most leaves as small, oval to irregular, dark brown to blackish spots that become enlarged with concentric rings. On microscopy, brownish muriform (9-11 transverse septa and 2-3 longitudinal septa) conidia in chains having almost hyaline beak were recorded that measured about 89.51-254.23 μm × 12.04-28.64 μm with an average size of 139.71 μm × 18.04 μm. All the fungicides tested (250, 500 and 1000 ppm concentrations) were effective against the pathogen when evaluated through poison food techniques in laboratory. Effectiveness of the fungicides was increased with the increase doses of fungicides. Indofil M-45 (96.30%) revealed superior where maximum inhibition of mean radial growth of the fungus was observed followed by Indofil Z-78 (94.44%), Merger (86.67%), Ishaan (84.44%), Foliogold (77.41%) and Infield Ayur (75.55%). Ethaboxam recorded ineffective and showed minimum (32.96%) inhibition. Fungicides used in field experiment were more or less efficacious. The highest disease reduction was recorded in Indofil M-45 (43.76%) followed by Indofil Z-78 (40.59%) and Merger (36.65%) over control whereas lowest of that was recorded in Ethaboxam (22.29%) and Infield Ayur (26.99%).