Variation in Suspected Cercospora Leaf Spot Incidence and Host Physiological and Fruit Traits Across Olive Tree Age Classes and Governorates in Palestinian Orchards

Cercospora leaf spot, caused by Pseudocercospora cladosporioides, is a defoliating disease of olive. Symptomatic leaf-spot incidence and physiological, biochemical, and fruit traits were assessed in nine rain-fed orchards located in Bethlehem, Hebron, and Ramallah, Palestine. The surveyed trees belonged to the grower-identified cultivar ‘Roumi’ and were assigned to three broad age ranges (Range I, 50–100 years; Range II, 25–50 years; Range III, 15–20 years), resulting in six governorate × age-range groups. Symptomatic leaves were collected from all surveyed orchards, and fungal isolates were obtained and characterized by macroscopic and microscopic observations. The observed morphological characteristics were consistent with Pseudocercospora cladosporioides, although molecular confirmation was not performed. Mean symptomatic leaf-spot incidence ranged from 9.29% in Hebron Range I to 14.11% in Bethlehem Range I, with overlapping distributions and no monotonic pattern across age ranges. Within the shared 25–50-year age range, mean incidence was similar among governorates (9.95–11.02%), whereas RWC, total chlorophyll, and fruit weight showed differences among governorates. Exploratory orchard- and group-level correlations showed no clear association between symptomatic incidence and measured host traits. The first two principal components accounted for 67.9% of the variation among the six aggregated group means (PC1 = 44.0%; PC2 = 23.9%), with symptomatic incidence showing a near-zero loading on PC1 (−0.05), providing no clear evidence of an association with the principal physiological gradient. These observations provide a descriptive baseline for monitoring suspected Cercospora leaf spot and support future balanced, age-resolved surveys with molecular pathogen confirmation.