Molecular Identification and Biological Activity of Verticillium lecanii Isolates Against Aphis gossypii in Greenhouse Cucumber

Abstract

Greenhouse cucumber production is frequently affected by the cotton aphid, Aphis gossypii, which causes direct feeding damage and acts as a vector of plant viruses. The present study evaluates the molecular identification and biological activity of Verticillium lecanii isolates against A. gossypii under greenhouse conditions. Fungal isolates were obtained from naturally infected insect hosts and cultured on selective media for morphological characterization, including colony morphology, conidial shape, and growth pattern. Molecular identification was performed using ITS rDNA sequencing, confirming the isolates as V. lecanii with high sequence similarity to reference strains. Laboratory bioassays were conducted using different conidial concentrations against nymphal and adult stages of A. gossypii, and mortality, infection rate, and sporulation on cadavers were recorded. Results demonstrated significant pathogenicity of selected isolates, with mortality increasing in a dose- and time-dependent manner. Early instar nymphs were more susceptible compared to adults, indicating stage-specific differences in vulnerability. Microscopic observations confirmed fungal attachment, germination, cuticle penetration, and internal colonization leading to host death. Greenhouse trials further validated the efficacy of the most virulent isolate, showing substantial reduction in aphid populations and minimal phytotoxic effects on cucumber plants. Environmental conditions such as high humidity significantly enhanced fungal infection and sporulation on host bodies. The study highlights the potential of V. lecanii as an effective mycoinsecticide for sustainable management of A. gossypii in protected cultivation systems. Overall, the findings demonstrate that molecularly characterized V. lecanii isolates possess strong biological activity and can be integrated into greenhouse pest management programs to reduce reliance on chemical insecticides.