ABSTRACT

Investigations on biosynthesis and evaluation of silver (AgNPs) and zinc nanoparticles (ZnNPs) synthesized using sweet flag rhizome extract against Sitophilus oryzae and Corcyra cephalonica in wheat were carried out at the University of Agricultural Sciences, Dharwad, Karnataka. The bioactive compounds present in the extract act as both reducing and stabilizing agents for synthesis of nanoparticles. AgNPs and ZnNPs showed maximum UV absorption peak of at 437 nm and 356 nm, respectively, with mean diameters of 42.08 nm and 32.68 nm. SEM images showed that AgNPs exhibited spherical to irregular shapes, while ZnNPs showed sheet-like to irregular shapes. EDX spectral images confirmed their elemental composition and XRD pattern indicated their crystalline nature. FTIR spectroscopy showed the involvement of organic groups responsible for capping and stabilizing the nanoparticles.
To standardize the concentrations for bioefficacy studies, different concentrations of AgNPs and ZnNPs ranging from 500 to 2500 ppm against S. oryzae and C. cephalonica were evaluated by observing mortality rates. As the concentration and days after treatment (DAT) increased, per cent mortality also increased. Among the different concentrations, AgNPs and ZnNPs both at 2500 ppm proved to be effective by recording cent per cent mortality against S. oryzae and C. cephalonica. Repellency tests showed higher efficacy for AgNPs compared to ZnNPs on S. oryzae.
Among silver and zinc nanoparticles, AgNPs at 2500 ppm was proved to be most effective against S. oryzae by completely inhibiting adult emergence, seed damage and weight loss up to 90 DAT during storage. This effectiveness was comparable to that of chemical check Deltamethrin. ZnNPs at 2500 ppm also resulted in least population buildup, seed damage and weight loss at 90 DAT. AgNPs additionally enhanced seed germination. Further, AgNPs and ZnNPs at 2500 ppm showed cent per cent mortality of C. cephalonica at 15 DAT.