Rapid Laboratory Evaluation of Fungicides against Phytophthora infestans Causing Late Blight of Potato

Aim: To develop method for rapid and simple laboratory evaluation of fungicides against Phytophthora infestans, the causal pathogen of late blight of potato.
Study Design: Descriptive statistics and analysis of variance. Each treatment was replicated thrice.
Place and Duration of Study: Department of Plant Protection, Palli-Siksha Bhavana (Institute of Agriculture), Visva-Bharati, India in February, 2014.
Methodology: Small portion of potato leaf tissue from advancing margin of late bight lesion is placed on water since Phytophthora infestans (Mont.) de Bary grow well in water producing hypha and sporangium. Using this property, performance of fungicides on mycelial growth and sporangia production/formation was assayed by placing a small bit of infected leaf tissue in different concentration of fungicides.
Results: Among the seventeen fungicides tested, chlorothalonil, fenamidone + mancozeb and tricyclazole inhibited mycelial growth and sporangia production but dimethomorph, tebuconazole + trifloxystrobin inhibited sporangia production only. Metalaxyl + mancozeb totally inhibited mycelial growth at higher concentration.
Conclusion: This method can be useful for evaluating and comparing performance of different fungicides and even same formulations of a fungicide, produced by different companies within a very short time period. The experimental work can be completed within 48 –72h if late blight infected leaves are available.