Morphological and Molecular Redescription of Rotylenchus spp. (Nematoda: Hoplolaimidae) Associated with Cereal Crops

Abstract

Tomato is one of the most widely cultivated vegetable crops worldwide, but its productivity is severely affected by fungal diseases, particularly under greenhouse cultivation systems where environmental conditions favor pathogen development. Stem rot caused by Didymella lycopersici has emerged as an important disease leading to stem lesions, tissue decay, wilting, and significant yield reduction in tomato crops. The present study was conducted to characterize and evaluate the pathogenicity of Didymella lycopersici associated with stem rot disease in greenhouse-grown tomato plants. Diseased tomato samples exhibiting typical stem rot symptoms were collected from commercial greenhouse production systems, and fungal isolates were obtained using standard isolation and culturing techniques. Morphological identification was performed based on colony characteristics and microscopic observations, while molecular characterization was conducted through polymerase chain reaction (PCR) amplification and sequencing of conserved genomic regions. Pathogenicity tests were carried out under controlled greenhouse conditions by inoculating healthy tomato plants with representative fungal isolates to confirm Koch’s postulates and assess disease severity. The results confirmed the association of D. lycopersici with stem rot symptoms in infected tomato plants. Considerable variation in virulence was observed among the tested isolates, with highly pathogenic strains causing extensive stem necrosis, wilting, and plant decline. Molecular analysis revealed close genetic similarity between the obtained isolates and previously reported D. lycopersici strains infecting tomato crops in other regions. The successful re-isolation of the pathogen from inoculated plants further verified its pathogenic role in disease development. This study provides important insights into the biology, pathogenicity, and molecular characteristics of D. lycopersici associated with tomato stem rot under greenhouse conditions. The findings emphasize the importance of early pathogen detection and integrated disease management strategies to reduce crop losses and improve the sustainability of greenhouse tomato production systems.