Survey and Pathogenicity of Pyrenochaeta lycopersici Causing Corky Root Rot on Tomato in Greenhouse Soils

Abstract

Corky root rot symptoms characterized by root browning, cortical cracking, reduced vigor, and stunted growth were frequently observed in greenhouse-grown tomato plants cultivated under intensive production systems. Surveys were conducted in major greenhouse tomato production areas to determine the distribution and incidence of the disease and to identify the associated causal pathogen. Diseased root samples collected from symptomatic plants were subjected to fungal isolation and characterization using morphological and pathogenicity analyses. Fungal isolates consistently produced slow-growing dark colonies with pycnidial structures and septate hyphae characteristic of Pyrenochaeta lycopersici. Disease incidence varied among surveyed greenhouses and was strongly influenced by soil moisture, cropping history, and greenhouse sanitation practices. Pathogenicity assays conducted under controlled greenhouse conditions reproduced typical corky root rot symptoms on healthy tomato seedlings, including root lesions, reduced root development, chlorosis, and plant wilting. Control plants remained symptom-free throughout the experimental period. Re-isolation of the pathogen from inoculated roots fulfilled Koch’s postulates and confirmed the pathogenic role of the isolates. Disease severity increased under conditions of continuous tomato cultivation and poorly drained soils, indicating that environmental and cultural factors significantly contribute to pathogen establishment and disease progression. Infected plants exhibited substantial reductions in biomass accumulation and root functionality, ultimately affecting plant productivity and fruit yield. The persistence of P. lycopersici in greenhouse soils and plant residues suggests a high potential for long-term survival and recurring disease outbreaks in protected cultivation systems.