Virulence and Molecular Characterization of Pseudomonas cichorii Causing Leaf Spot on Lettuce in Hydroponic Systems

Abstract

Lettuce is one of the most important leafy vegetables cultivated in hydroponic production systems due to its high market demand and rapid growth cycle. However, bacterial diseases significantly threaten productivity and quality under protected cultivation environments. Among these, leaf spot disease caused by Pseudomonas cichorii has emerged as a serious concern, leading to water-soaked lesions, necrotic spots, chlorosis, and reduced marketability of lettuce leaves. The present study was conducted to investigate the virulence and molecular characteristics of P. cichorii associated with leaf spot disease in hydroponically grown lettuce. Symptomatic lettuce samples were collected from commercial hydroponic facilities, and bacterial isolates were obtained using standard microbiological isolation techniques. Morphological and biochemical characterization of isolates was performed, followed by molecular identification using polymerase chain reaction (PCR) amplification and sequencing of conserved genetic regions. Pathogenicity assays were carried out under controlled environmental conditions by inoculating healthy lettuce plants to confirm the causal role of the bacterium and evaluate virulence variability among isolates. The results confirmed the consistent association of P. cichorii with symptomatic lettuce tissues collected from hydroponic systems. Inoculated plants developed typical leaf spot symptoms, including necrotic lesions and tissue collapse, thereby fulfilling Koch’s postulates. Considerable variation in virulence was observed among the tested isolates, with highly aggressive strains causing rapid disease progression and severe leaf damage. Molecular sequence analysis revealed high genetic similarity between the obtained isolates and previously reported P. cichorii strains infecting leafy vegetables in different regions. Environmental conditions characterized by high humidity and dense plant spacing within hydroponic systems were found to favor disease development and spread. The findings of this study provide important insights into the pathogenicity and molecular diversity of P. cichorii affecting lettuce under hydroponic cultivation. Early diagnosis and implementation of integrated disease management practices are essential for minimizing economic losses and ensuring sustainable hydroponic lettuce production.