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Fungicide sensitivity of the Indian sub-clonal variants of the Phytophthora infestans 13_A2 lineage

Sanjoy Guha Roy: West Bengal State University

<div><em>Phytophthora infestans</em> is a highly adapted oomycete pathogen of potato and tomato, aggressive genotypes of which often migrate to a new geographical region causing huge crop losses. Large sub-clonal variations within the European 13_A2 (blue 13) lineage were recently identified from a severe late blight epidemic in Eastern India in 2014. The fungicide sensitivity of these GPS-tagged and characterised populations (n=59) was carried out to determine the baseline sensitivity against the active ingredients of the five commercial fungicides Curzate<strong>® </strong>M-8 (Cymoxanil 8% + Mancozeb 64%), Indofil M- 45 (Mancozeb 75%), Acrobat<strong>® </strong>(Dimethomorph 50%), Amistar<strong>® </strong>(Azoxystrobin 23% ) and Aliette<strong>® </strong>(Fostyl- al 80%)<strong>. </strong>The fungicide sensitivity data was examined in relation to the 24 Multi Locus Genotypes (MLGs) derived from our previous studies and host (potato and tomato). Dose response and EC<sub>50 </sub>values were calculated for each isolate using an <em>in vitro</em> agar growth assay with 5-6 doses. No insensitivity was observed for any fungicide as the EC<sub>50 </sub>values were within the range of prescribed field doses for each fungicide. Among these fungicides, Amistar<strong>®</strong> has the lowest EC<sub>50</sub> value < 0.1 ug/ml in all isolates. Minor variation in relation to host and MLG was observed and will be related to prior management practices. This baseline sensitivity information for this region will help growers manage their use of fungicides for effective control of this exotic pathogen population.</div>