Silver nanoparticles green synthesized using leaf extract of Piper spp. reduce Phytophthora capsici infection in black pepper (Piper nigrum L.)

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Black pepper (Piper nigrum L.) is vulnerable to the devastating disease foot rot caused by the oomycete, Phytophthora capsici. Green synthesis of nanoparticles using plant extracts provides an eco-friendly, and economical method for plant disease management. Leaf extracts from two genotypes of pepper plants - one susceptible to foot rot disease (P. capsici) - Piper nigrum, and the other, resistant - Piper colubrinum, were used for synthesizing silver nanoparticles (AgNPs). These green synthesized AgNPs were characterized and evaluated for their anti-oomycete effects against P. capsici and ability to suppress foot rot disease in black pepper. UV Spectroscopic analysis confirmed typical absorption characteristics of AgNPs, while field emission scanning electron microscopy revealed sizes ranging from 39 to 69 nm for both samples. In vitro poisoned food assay demonstrated that the green synthesized AgNPs at 500 and 750 ppm showed highest inhibition on the mycelial growth of the pathogen. Among the treatments,71% and 77% inhibition in mycelial growth of pathogen was observed with 500 ppm and 750 ppm of Pn-AgNPs respectively, and 65% and 73% inhibition in growth of mycelia of pathogen with 500 ppm and 750 ppm of Pc-AgNPs respectively. Copper Oxychloride at 0.2% completely inhibited mycelial growth. In a detached leaf assay with black pepper variety Panniyur-1, significant reduction in lesion development was observed on leaves treated with the green synthesized AgNPs compared to those treated with commercial AgNPs and chitosan nanoparticles. No lesion developed on leaves treated with 750 ppm concentration of green synthesized AgNPs. Leaf extracts were ineffective in disease suppression and pathogen growth. Mild symptoms were observed on leaves treated with the biocontrol agent (Pseudomonas fluorescens, 2%), while no symptoms were found on leaves treated with the fungicide. Spraying of AgNPs green synthesized using leaf extracts of pepper genotypes reduced foot rot disease incidence in susceptible pepper genotype P. nigrum, efficiently. Green nanotechnology for foot rot management can benefit farmers by providing an eco-friendly, cost-effective solution that reduces dependency on chemical fungicides and minimizes environmental impact.