Mycobiome-linked metabolomic changes reveal two cultivar-specific defense modes in field-infected date palm leaves

Early detection of foliar fungal disease in date palm (Phoenix dactylifera L.) is essential for timely intervention, yet physiological markers preceding visible symptoms remain poorly defined. Here, we combined fungal isolation and pathogenicity testing with untargeted GC-TOF-MS profiling of symptomatic (S) and asymptomatic (AS) leaves from four cultivars (Medjool, Sukkari, Khalas, and Khenaizi) under natural field infection. Among 103 fungal isolates, 15 were confirmed as pathogenic in detached-leaf assays, with Alternaria spp. predominating. Notably, several species, including Alternaria prunicola, Curvularia beasleyi, and Bipolaris sorokiniana, are reported here for the first time in association with date palm pathology. Metabolomic analysis revealed two cultivar-dependent response modes. Mode A, dominant in Medjool and Sukkari, was characterized by sugar reallocation, including broad hexose depletion, notably α-DL-glucopyranoside, together with an early decline in malonic acid, consistent with increased glycolytic and pentose phosphate pathway demand for defense and redox buffering. Mode B, dominant in Khalas and Khenaizi, reflected lipid-antioxidant remodeling, with increases in α-tocopherol and β-sitosterol and selective terpenoid rewiring, consistent with membrane stabilization and oxidative-stress control. PCA separated S from AS samples, while PLS-DA resolved classes with significant permutation support; VIP rankings converged with large standardized effects (Hedges' g) on a concise set of discriminant metabolites. These results establish a cultivar-resolved, field-realistic framework linking pathogen context to two distinct metabolic defense trajectories in date palms. This study identifies a list of candidate biomarkers for early fungal disease detection and provides a physiological basis for trait-aware monitoring and management of date palms under arid agricultural conditions.