THE NATURE OF RESISTANCE OF SOME PEPPER CULTIVARS TO POWDERY MILDEW DISEASE CAUSED BY Leveillula taurica (LEV.) ARN. UNDER GREENHOUSE CONDITIONS

This work was carried out under green house conditions at Tokh and Sakha during 2007and 2008. All tested pepper cultivars differed in their response to Leveillula taurica infection at Tokh and Sakha locations .Gedeon F₁ cv. was very susceptible (71.93 %),while Parma cv. was the least susceptible one    (9.78 %). The highest values of the area under disease progress curve ( AUDPC) and rate of powdery mildew increase (r-value) were recorded with the highly susceptible cultivars Gedeon F₁followed by panta F₁, while the lowest values in this respect were in the least susceptible Maro and Parma cv. In addition,  Parma cv . was found superior to all cultivars with respect to fresh weight (612.1 & 634.5 g/plnt), dry  eight 129.7&132.6  g/plant)  and fruit yield (65.8 & 68.6 kg/polt ) at Tokh and Sakha .A positive correlation was found between pepper susceptibility to the infection with L. taurica and the number of stomata on both leaf surface. Gedeon F1 cv. with an average (181.72 & 385.74stomat/cm²) on upper and lower leaf surfaces was found highly susceptible. Parma cv. was less susceptible and showed (24.15 &131.26 stomat / cm²) . Both chlorophyll a , b and carotene contents in healthy of the least susceptible Parma cv. was higher than that of the highly susceptible Gedeon F1 cv. L.taurica infection decreased the content of chlorophyll and carotene in both cultivars and total sugars and free amino acids were higher in the healthy plants of the least susceptible cultivar than that in the highly susceptible one, L. taurica infection reduced the total sugars and free amino acids in both cultivars. The total phenols was higher in leaves of the highly susceptible cultivar than that in the least susceptible one. The activity of oxidative enzymes peroxidase, polyphenoloxidase and catalase increased in the least susceptible Parma cv. than in the highly susceptible Gedeon F1 cv. L. taurica infection lead to an increase in the levels of oxidative enzymes in the infected leaves as  compared to with the healthy ones.