Silver nanoparticles synthesized from Coleus scutellarioides leaf extract exhibit antimicrobial activity against bacterial and fungal pathogens of fruit crops

Green synthesis of metal nanoparticles using plant-derived reducing and stabilizing agents offers an environmentally compatible alternative to chemical synthesis. However, developing multifunctional nano-enabled microbicides that are both effective and safe for crop systems remains a challenge. To provide a simple and sustainable approach for managing fruit crop diseases, this study utilized Coleus scutellarioides leaf extract to synthesize silver nanoparticles (AgNPs) and evaluated their antimicrobial activities against two major phytopathogens infecting herbaceous (tomato) and woody (bayberry) crops. The plant extract efficiently mediated the formation of uniform, spherical AgNPs with an average diameter of 36.4 nm, confirmed by spectroscopic and microscopic analyses. The nanoparticles significantly inhibited the growth of Pseudomonas syringae pv. tomato (Pst) by 66% at 100 µg/mL and reduced bacterial motility and biofilm formation. Strong antifungal activity was also observed, with more than 72% inhibition of Pestalotiopsis versicolor mycelial growth at 500 µg/mL in both solid and liquid media. Microscopic and biochemical assays showed that the nanoparticles disrupted microbial cell membranes and compromised cellular integrity. Detached-leaf assays further demonstrated that AgNPs pre-treatment significantly reduced tomato bacterial speck and bayberry twig blight severity, with disease suppression comparable to that of conventional copper-based bactericides and commercial fungicides. Furthermore, the nanoparticles exhibited no phytotoxic effects on rice seed germination at 250 µg/mL, indicating good biocompatibility for agricultural applications. This plant-mediated synthesis provides a green, simple, and scalable method for synthesizing antimicrobial AgNPs without chemical reagents. The resulting nanoparticles exhibit broad-spectrum antimicrobial activity against bacterial and fungal pathogens in both herbaceous and woody fruit crops. These findings highlight their potential as sustainable nano-enabled microbicides for integrated disease management in agriculture.