Bioefficacy of Fungicides Against Phytophthora infestans Causing Late Blight of Potato under Laboratory Condition

The experiment was conducted in laboratory in aqueous environment to evaluate bioefficacy of fungicides against Phytophthora infestans (Mont.) de Bary causing late blight of potato (Solanum tuberosum L.) during February, 2015. Infected leaves of potato var. Kufri Jyoti were collected from field in morning hours, cut into small pieces (1.0cm x 0.5cm), and were placed in petriplates containing fungicides suspension (0.1, 0.05 and 0.025%) and sterile filtered tap water. The plates were incubated at room temperature for 48 h and observed under microscope. Derosal (carbendazim) and Shine-35 (metalaxyl) showed very negligible or little effect. However, metalaxyl when associated with mancozeb (Matco) inhibited mycelial growth and sporangia formation. Blitox (copper oxychloride), Avtar (hexaconazole + zineb) and Vitavax Power (Carboxin + Thiram) inhibited mycelial growth only at higher concentration. Adequate inhibition of mycelial growth and sporangia formation was recorded in Indofil Z-78 (zineb), Indofil M-45 (mancozeb), Mirador (azoxystrobin), Acrobat (dimethomorph) and Melody Duo (Iprovalicarb + Propineb). Highest inhibition of both mycelial growth and sporangia formation were evidenced in Ethaboxam (a thiazole carboxamide fungicide) followed by FolioGold (Chlorothalonil + Metalaxyl) and Kavach (Chlorothalonil). This rapid laboratory evaluation method is truly useful to select effective fungicide(s) against late blight of potato quickly within 48-72 h.