Comparative in vitro evaluation of fungicides against collar rot pathogen, Sclerotium rolfsii in elephant foot yam

Amorphophallus or elephant foot yam (Amorphophallus paeoniifolius) popularly known as the ‘King of tubers’ is one of the major tuber crops grown in India and other parts of the world. Collar rot disease, caused by Sclerotium rolfsii is one of the primary obstacles to tuber cultivation which can significantly reduce yield up to 100%. Saprophytic nature, broad host range, and ability to produce resting structures make it difficult to manage. In this experiment, 10 isolates of S. rolfsii were isolated by the surveying Thiruvananthapuram, Kollam and Alappuzha districts of Kerala, proved the pathogenicity by inoculating the pathogen cultured in sand- maize meal media (9:1). The isolate I3 obtained from Thiruvananthapuram district was found to be the most virulent based on the days taken for symptom development (4 days). Six fungicides (copper oxy chloride (50% WP), mancozeb (75% WP), propiconazole (25% EC), carbendazim (50% WP), trifloxystrobin (25%) + tebuconazole (50%) 75 WG, and carbendazim (12%) + mancozeb (63%) WP @ 50, 100, 250, 500, 1000 and 2000 ppm were evaluated in vitro for their efficacy in inhibiting the fungal mycelial growth and sclerotia formation in isolate I3. All fungicides except carbendazim 50% WP and copper oxy chloride 50% WP, considerably reduced the mycelial development of S. rolfsii. Mancozeb 75%WP and trifloxystrobin (25%) + tebuconazole (50%) 75WG, showed complete inhibition of mycelial growth even at a lower concentration of 50 ppm.