Mating type, Metalaxyl Resistance and Aggressiveness of Phytophthora infestans (Mont.) de Bary in Morocco

Ninety-nine isolates of Phytophthora infestans collected from different locations in Morocco were characterized using mating type (A1 and A2) and metalaxyl resistance markers (MS, metalaxyl sensitive, MRS, reduced metalaxyl sensitive, MMR, moderately metalaxyl resistant, MR, metalaxyl resistant). Aggressiveness of these isolates was assessed on detached potato and on detached tomato leaves by determining the lesion size and the sporulation capacity. Characterization of these isolates revealed the following distribution: 29% of the isolates were A1-MS, 5% were A1-MRS, 5% were A1-MMR, 2% were A1-MR, 20% were A2-MS, 10% were A2-MRS, 21% were A2-MMR and 8% were A2-MR. Significant differences in aggressiveness were found among isolates. A tendency for MMR and MR isolates to be more aggressive (larger lesions and higher sporulation capacity) than the MRS and MS isolates was found. Potato isolates were more aggressive on potato than tomato isolates, whereas both potato and tomato isolates were comparable concerning their aggressiveness on tomato. This study demonstrates a heterogeneity of Moroccan P. infestans populations.