In vitro and in vivo fungicidal effects of γ-irradiation synthesized silver nanoparticles against Phytophthora capsici causing the foot rot disease on pepper plant

γ-rays irradiation, is a powerful method for the preparation of colloidal silver nanoparticles (AgNPs). Three different AgNPs with average particle size of 5, 10 and 15 nm were synthesized and stabilized by chitosan (1%), and demonstrated a significant in vitro activities against Phytophthora capsici with 62.5, 84.3 and 100%, inhibition efficacy, respectively. An improved antifungal activity of 10 nm size AgNP was noticed by increasing the initial silver concentration with maximum inhibition efficiency of 92.9% at 100 ppm. The in vivo study performed for fungicidal effect of AgNPs in pepper plants showed that pretreatment of 1–10 ppm AgNPs effectively reduced P. capsici infection leading to enhanced rate of non-disease-outbreak of 53.3 and 95.0%, respectively. On the other hand plants treated with AgNPs after fungus infection displayed 60.0 and 91.7% non-disease-outbreak after the treatment at 10 and 50 ppm concentration, respectively. The results specify the potential role of γ-irradiation synthesized AgNPs for controlling the pathogen P. capsici on black peppers. Moreover, the environmental friendly production of AgNPs and its high effectiveness against fungi prove it a safe and alternative against the conventional antifungal agents.