A Review of Metalaxyl Resistance in Phytophthora infestans from Pakistan

Late blight is a serious disease of potato in Pakistan. Systemic fungicides like metalaxyl and other related compounds are being widely used for late blight control. Understanding the population structure of Phytophthora infestans in terms of metalaxyl sensitivity is important for developing sound management strategies for this disease. Three distinct studies have assessed the metalaxyl resistance in P. infestans in Pakistan since 1997. From 1997 to 2000, most isolates were intermediately resistant. In 2003-2004, slightly more than half of the isolates were resistant, with 31% being intermediately resistant and 15% being sensitive. During 2006-2007 all of 120 isolates were resistant to metalaxyl. Continuous monitoring of metalaxyl resistance is necessary to develop sound disease management approaches.