Evaluation of fungicides on Indian isolates of Phytophthora colocasiae causing leaf blight of taro

Leaf blight caused by Phytophthora colocasiae is the most destructive disease affecting taro (Colocasia esculenta) worldwide including India. Fungicides (primarily metalaxyl) remain as an important strategy to manage taro leaf blight in India over decades. It is important to monitor isolate sensitivity to identify build-up of fungicide resistance and thereby modify fungicide usage strategies. P. colocasiae isolates representing four different geographical regions of India were evaluated for their sensitivity to metalaxyl and three other commercially available fungicides viz. Samarth, Biofight and Akoton by poisoned media technique. All the isolates tested were sensitive to metalaxyl, nevertheless there is an increase in the effective concentration compared to the previous reports. Among the other fungicides, Samarth was found to be superior in completely inhibiting mycelial growth at 0.05% followed by Biofight at 1%. Metalaxyl and Akoton® shared a common inhibitory concentration at 2%. The most effective fungicide determined by the in vitro method was evaluated in vivo for studying the pattern of inhibition before and after the disease development in detached taro leaf. The results of the study revealed that build-up on metalaxyl resistance in P. colocasiae is in its course and caution should be taken while administering against taro leaf blight. Fungicide Samarth could be used as an alternative to metalaxyl for management of taro leaf blight.