Endophytic colonization by Beauveria bassiana and Metarhizium anisopliae induces growth promotion effect and increases the resistance of cucumber plants against Aphis gossypii

Abstract

The entomopathogenic fungi (EPF) are characterized as fungi with various functions and numerous mechanisms of action. The ability to establish themselves as beneficial endo-phytes provides a sound ground for their exploitation in crop production and protection. The purpose of this study was to evaluate the entomopathogenic strains of Beauveria bas­ siana and Mertarhizium anisopliae for their potential to colonize cucumber plants under natural environmental conditions in non-sterile substrate. Seed submersion in conidial suspension resulted in systemic colonization of cucumber plants 28 days post-inoculation. Scanning electron microscope micrographs demonstrated that conidia of both fungal genera have adhered, germinated and directly penetrated seed epidermal cells 24 hr post-sub-mersion. Treated with EPF cucumber seeds resulted seedlings tissues of which contained a significantly higher amount of total phenolic compounds and unchanged amounts of chlorophylls. There was a significant negative effect of endophytic colonization on the Aphis gossypii population size after 5 days of exposure as well as a positive effect on cucumber growth and development 7 weeks post-inoculation. We suggest that reduction of A. gossypii population on mature Cucumis sativus plants is caused via an endophyte-triggered improvement of plant’s physiological parameters such as enhanced plant growth with subsequent increase in plant resistance through augmented production of phenolic compounds.