ECOLOGY Susceptibility of Apple Varieties to Tetranychus urticae Koch and Panonychus ulmi Koch and its Relation to the Nutrient Contents and Spider Mite Predators in Apple Trees

El-Abdallah, J., M. Muflih and L.H. Aslan. 2022. Susceptibility of Apple Varieties to Tetranychus urticae Koch and Panonychus ulmi Koch and its Relation to the Nutrient Contents and Spider Mite Predators in Apple Trees. Arab Journal of Plant Protection, 40(2): 119-126. https://doi.org/10.22268/AJPP-40.2.119126 The susceptibility to T. urticae and P. ulmi of eight apple varaietis were studied in southern Syria (Sweida) from 2018 to 2020. Significant differences of susceptibility to the two species between apple varieties, in addition to significant differences of apple-leaf nutrients content (NPK) were found. Results obtained showed that apple-leaf nutrients content affect the susceptibility to the two spider mite species differently. Principal component analysis (PCA) showed positive correlation to P. ulmi with apple-leaf contents of potassium and negative correlation with apple-leaf contents of nitrogen and showed positive correlation between T. urticae numbers and nitrogen and phosphorous content. T. urticae had a weak correlation with potassium apple-leaf content in 2019. Cluster analysis showed that apple varieties were distributed in three clusters based on the studied factors in 2020. The first cluster included the varieties Top Red, Starking Delicious and Starking Red Delicious which were the most sensitive to P. ulmi. The second cluster included Golden Delicious, Golden 972 and Granny Smith, and those were less sensitive to P. ulmi and the third cluster included Ozark Gold and Royal Red and these varieties were moderately sensitive to P. ulmi. The effects of studied factors were clearer on P. ulmi than on T. urticae. Keywords: Apple, T. urticae, P. ulmi, Phytoseiidae, Principal component analysis, PCA.