Biosynthesis and antifungal activity of silver nanoparticles against ​Nigrospora oryzae

Abstract

Fungal diseases substantially constrain potato production by impairing fundamental physiological processes. In greenhouse-grown seedlings, Nigrospora oryzae (N. oryzae) was identified as the etiological agent responsible for characteristic brown foliar lesions. In this study, silver nanoparticles (AgNPs) were synthesized through a one-step biosynthetic approach. The synthesis employed metabolites of N. oryzae together with AgNO₃ as precursors. The optimal synthesis parameters were established as 0.08 ​mol/L AgNO₃, a mycelial surface area of 15.708 ​cm², and a reaction temperature of 70 ​°C. Structural characterization using UV–Vis spectroscopy and X-ray diffraction (XRD) confirmed the formation of highly pure AgNPs. These particles were predominantly oriented along the (111) crystal plane and exhibited strong UV resistance and thermal stability. The biosynthesized AgNPs demonstrated pronounced antifungal efficacy. At 600 ​mg/L, they achieved an inhibition rate of 48.47 ​%. The EC₅₀ value was 625.23 ​± ​15.75 ​mg/L. Biochemical analyses indicated oxidative stress, as evidenced by elevated reactive oxygen species (ROS) and MDA levels, hyphal morphological abnormalities, suppression of physiological activity, and subsequent cell death. Furthermore, DNA integrity was impaired, as reflected by darker and narrower electrophoretic bands at the 600 ​mg/L. Pot experiments revealed that AgNP treatment at 500 ​mg/L reduced the disease index by 75.34 ​%. The 96-h acute toxicity test on aquatic organisms also indicated that the toxicity of AgNPs was relatively low. Collectively, these findings demonstrate the potential of biosynthesized AgNPs as an environmentally sustainable strategy. They represent a highly effective option for managing potato fungal diseases, particularly those caused by N. oryzae under greenhouse conditions.