In vitro Evaluation of Fungicidal Efficacy against Sclerotium rolfsii in Soybean

Aim: To assess the efficacy of newly approved and recommended fungicides in controlling collar rot disease of soybean under In vitro conditions. Study Design: In vitro assessment of fungicide efficacy and statistical analysis of mycelial inhibition percentage of collar rot fungus. Place of Study: Division of Crop Protection, ICAR-National Institute of Soybean Research, Khandwa Road, Indore. Methodology: Infected plant samples were collected to isolate collar rot fungi and cultured on Potato Dextrose Agar (PDA). The Sclerotium rolfsii isolate displayed white, cottony mycelium and brown sclerotia (Approximately 0.32 mm). Sclerotia were transferred to PDA plates acidified with 0.2% lactic acid to establish a pure culture, with weekly sub-culturing for maintenance of the pathogen S. rolfsii. Fungicide efficacy was assessed by adopting poison food technique. PDA plates were amended with fungicides registered in India, including foliar fungicides (picoxystrobin, hexaconazole, pyraclostrobin + epoxiconazole, kresoxim-methyl, propiconazole, picoxystrobin + propiconazole, tebuconazole) at 0.05%, 0.1%, 0.15%, and 0.2%, and seed treatment fungicides (thiophanate methyl + pyraclostrobin, penflufen + trifloxystrobin, carboxin + thiram, carbendazim + mancozeb) at four different concentrations viz., 0.025%, 0.05%, 0.1%, and 0.125%. A Mycelial disc measuring 4 mm from a 4-day-old culture was placed in the centre of poisoned PDA plates, incubated at 26 ± 1°C with a 14h light/10h dark cycle. Mycelial growth inhibition was calculated using Vincent’s formula. Results: The analysis showed significant differences in growth inhibition among fungicides (P < 0.0001), concentrations (P < 0.0001), and their interaction (P < 0.0001) for foliar applications, but no significant differences for seed dressing fungicides. In foliar applications, a 0.125% concentration (72.39%) was more effective than lower concentrations, with tebuconazole (100.00%) showing the highest inhibition of S. rolfsii. For seed dressing, all fungicides at all concentrations completely suppressed mycelial growth (100.00%) of S. rolfsii. Conclusion: Tebuconazole effectively controlled S. rolfsii as foliar applications, while seed treatments with thiophanate methyl + pyraclostrobin, penflufen + trifloxystrobin, carboxin + thiram, and carbendazim + mancozeb completely inhibited mycelial growth. Further field studies are to be conducted to confirm their practical efficacy in managing collar rot in soybean.