AGGRESSIVENESS AND SENSITIVITY TO METALAXYL OF PHYTOPHTHORA INFESTANS ISOLATES FROM CAMEROON

Isolates of Phytophthora infestans were obtained from diverse hosts (potato, tomato and garden huckleberry) in Cameroon and assessed for aggressiveness and sensitivity to metalaxyl in replicated in vitro experiments. Aggressiveness tests were conducted on detached leaves and metalaxyl sensitivity was determined on leaf disks. Inoculated leaves and disks were incubated in Petri dishes in temperature chambers at 18°C for 7-8 days, 12h daylight. The P. infestans isolates derived from potato and tomato were more aggressive than those isolated from huckleberry. The average lesion area on inoculated leaves ranged from 17 to 41%, 13 to 38% and 5 to 16% on potato, tomato and huckleberry, respectively. Variation in the sensitivity of P. infestans isolates to metalaxyl was recorded, depending on the geographic and host origins of the isolates. Resistance to metalaxyl was detected in 49.0 and 50.3% of the isolates in 2001 and 2002, respectively. Resistance to metalaxyl was greatest on isolates derived from tomato and least on those obtained from huckleberry. We discussed how assessment of metalaxyl resistance and aggressiveness among pathogen isolates would be useful for effective management of P. infestans in Cameroon.