Characterization of sordaria macrospora causing leaf tip blight in olive (olea europaea L.) trees, investigation of control strategies, and determination of plant defense responses

Olive (Olea europaea L.), a member of the Oleaceae family, is an important crop predominantly adapted to the Mediterranean climate. Recently, symptoms such as leaf tip burn, shoot dieback, and backward death have been observed on olive trees in the Southeastern Anatolia Region of Turkey. In this study, surveys conducted in the region led to the isolation of numerous fungal species, among which six isolates showed morphological and microscopic characteristics similar to Sordaria macrospora. PCR amplifications were performed on these isolates targeting the ITS (ITS4/ITS6), LSU (NL1/NL4), β-tubulin (Bt2a/Bt2b), and Tef-1α (EF728F/EF986R) gene regions. The obtained sequences were submitted to the NCBI database, and the isolates were found to share 99–100% similarity with S. macrospora. Phylogenetic relationships with other global strains were determined by constructing a phylogenetic tree. Pathogenicity tests were conducted with a representative isolate, and successful re-isolation confirmed the pathogenic nature of the fungus. Additionally, the protease and laccase enzyme activities of the fungus were analyzed, revealing in vitro pathogenic properties. In a multi-stress experiment, two olive cultivars (Manzanilla and Arbequina) were subjected to different salt concentrations (50 mM and 100 mM) in the presence of the pathogen (S. macrospora), and symptom severity along with stress-related physiological parameters were evaluated. The results indicated that increasing salt concentrations amplified disease severity, and this effect was further intensified in the presence of the pathogen, correlating with reductions in physiological parameter values. Cultivar susceptibility varied according to the measured parameters. Furthermore, the effectiveness of seven different fungicides and the biological agent Trichoderma harzianum against S. macrospora was evaluated. Four fungicides exhibited fungicidal, while one showed fungistatic effects. Specifically, formulations containing 200 g/L Azoxystrobin + 80 g/L Cyproconazole (Amistar Xtra), 250 g/L Prochloraz + 75 g/L Trifloxystrobin + 50 g/L Cyproconazole (Basking), 200 g/L Azoxystrobin + 125 g/L Difenoconazole (Aquatis), and 25.2% Boscalid + 12.8% Pyraclostrobin (Bellis) demonstrated fungicidal activity, completely inhibiting mycelial growth. Pyraclostrobin + Fluxapyroxad (Priaxor) exhibited fungistatic effects. In contrast, formulations containing 300 g/L Phosphorous Acid + 75 g/L Ametoctradin (Privest) and 500 g/L Metrafenone (Vivando) did not inhibit mycelial growth. Moreover, applications of Trichoderma harzianum showed significant antagonistic effects. This study represents the first report of Sordaria macrospora as a pathogen on olive trees and provides a comprehensive investigation of its biology, host–pathogen interactions, and management strategies, offering pioneering insights into integrated disease control.