First Report of Passalora fulva Causing Leaf Mold on Tomato in Open-Field Production Under High Humidity

Abstract

Leaf mold symptoms characterized by pale yellow chlorotic spots on the upper leaf surface and olive-green to brown velvety fungal growth on the lower surface were observed in tomato (Solanum lycopersicum) cultivated under open-field high humidity conditions, leading to reduced photosynthetic efficiency and yield losses. Diseased leaf samples collected from affected fields were used for pathogen isolation and characterization through morphological, pathogenicity, and molecular approaches. Fungal isolates consistently produced slow-growing olivaceous colonies with septate hyphae and dense conidiophores bearing branched chains of conidia typical of Passalora fulva. Considerable variation in colony morphology, sporulation intensity, and lesion development was observed among isolates obtained from different tomato-growing locations. Pathogenicity tests conducted on healthy tomato plants reproduced characteristic leaf mold symptoms, including chlorotic spotting and velvety sporulation, whereas control plants remained symptom-free. Re-isolation of the fungus from inoculated tissues fulfilled Koch’s postulates, confirming its pathogenic role. Molecular identification was performed using amplification and sequencing of the internal transcribed spacer (ITS) region along with additional conserved loci relevant for fungal phylogeny. Sequence analysis revealed high similarity with authenticated P. fulva isolates available in global databases. Phylogenetic analysis grouped field isolates within the P. fulva clade with strong bootstrap support, confirming species identity. High humidity conditions, prolonged leaf wetness, and moderate temperatures were found to strongly favor infection, sporulation, and disease spread in open-field production systems. Severe infections resulted in significant reduction in leaf area, photosynthetic activity, and overall plant productivity.