Resistance of Phytophthora infestans to metalaxyl and the strategy for control

The causal agent of late blight of tomato,Phytophthora infestans was isolated from tomato leaves and fruits collected from Bisshan and Shapingba in 2000 and 2001.A total of 80 isolates were obtained and tested for fungicide resistance and resistance level to metalaxyl by measuring the growth of the fungal colony.Results showed 71.4?% isolstes were resistant,15.7?% isolates were intermediate in resistance and 12.9?% isolates were sensitive to metalaxyl.The resistance levels of the four tested resistant isolates were much higher than that of the metalaxyl -sensitive isolate(TBS-2131).The strategy for applying pesticide was put forward in connection with these areas.