Physiological effects of nanosilver on vegetative mycelium, conidia and the development of the entomopathogenic fungus, Isaria fumosorosea

Abstract

An assessment of the influence of water nanosilver suspension was made at a concentration of 10 mg·L−1 on biological material (i.e., vegetative mycelium and conidia of Isaria fumosorosea entomopathogen) on a background of the silver nitrate ionic form used. Conidia of I. fumosorosea treated with silver nitrate for more than 168 h were completely deactivated. The application of nanosilver on Isaria hyphae resulted in a quantitative limitation of mycelium growth and its weaker sporulation after culturing compared to the control. The pathogenicity of a conidial suspension obtained from such culturing towards test insects did not diverge from that observed in the standard culture. No obvious toxic effects of nanosilver were observed on I. fumosorosea conidia. Isaria conidia, after exposure to nanosilver over a period between 1 and 800 h, initially demonstrated weaker vegetative mycelium formation in culture on solid medium and, as a consequence, this mycelium often sporulated in a poorer manner. In one case, there was a significant stimulation of the sporulation process for nanosilver treatment before culture for 168 h. Concurrently, conidial suspensions obtained from the culture after exposure of over 168 h to nanosilver exhibited enhanced pathogenicity towards test insects, which may be considered a beneficial phenomenon in terms of the function played by Isaria in the whole environment. The reaction of conidia with nanosilver indicates the deactivation of conidia cells in suspensions and a possibility of selection in increased pathogenicity.