Morphological Variability and Molecular Phylogeny of Stemphylium Species on Tomato in Arid Agricultural Zones

Abstract

Species of Stemphylium are important fungal pathogens associated with leaf spot and blight diseases in tomato, causing significant reductions in crop productivity under favorable environmental conditions. Accurate identification and understanding of phylogenetic relationships among Stemphylium species are essential for effective disease diagnosis and management, particularly in arid agricultural zones where environmental stress influences pathogen diversity. The present study investigated the morphological variability and molecular phylogeny of Stemphylium species isolated from infected tomato plants collected from arid production regions. Fungal isolates were characterized based on colony morphology, pigmentation, conidial size and shape, septation patterns, and sporulation behavior under laboratory conditions. Considerable variability in morphological characteristics was observed among the collected isolates, indicating phenotypic diversity within the pathogen population. Molecular characterization was conducted using internal transcribed spacer (ITS) and other conserved genomic regions followed by sequence analysis and phylogenetic reconstruction. Phylogenetic analysis revealed the presence of genetically distinct Stemphylium species associated with tomato crops in arid agricultural environments. Certain isolates formed closely related clusters, whereas others exhibited substantial genetic divergence, suggesting adaptation to local environmental conditions and host interactions. The integration of morphological and molecular approaches improved the accuracy of species identification and clarified taxonomic relationships among closely related isolates. Environmental factors characteristic of arid regions, including high temperature and low humidity, were found to influence pathogen distribution and variability. The findings provide valuable insights into the diversity and evolutionary relationships of Stemphylium species affecting tomato crops and support the development of effective disease monitoring and integrated management strategies for sustainable tomato production in arid agroecosystems.