Physiological Responses of Two Varieties of Common Bean (Phaseolus vulgaris L.) to Foliar Application of Silver Nanoparticles

This study reported the synthesis of aqueous dispersions of highly stable silver nanoparticles (AgNPs) using gamma radiation with gum acacia (GA) as the stabilizing and protecting agent. The formation of nanosized silver GA-gNPs at a gamma irradiation dose of 15 kGy was confirmed by the appearance of the characteristic surface plasmon absorption peak at 456 nm and in UV-vis spectra. The particle size distribution of silver nanoparticles that was determined by Dynamic Light Scattering (DLS) was approximately 22 nm. By using Transmission Electron Microscopy (TEM), mostly spherical GA-AgNPs particles with a mean diameter of 16.7 nm and crystalline in shape were confirmed by an X-ray diffraction (XRD) pattern. Fourier Transform Infrared (FTIR) spectroscopic analysis indicates the bonding of AgNPs with the COO-group of gum acacia. To increase our understanding of the mechanisms involved in plant responses to GA-AgNPs and AgNO3, in order to differentiate between particle-specific and ionic-silver effects, we determined the response of vegetative growth and the yield of two varieties (Bronco and Nebraska) of the common bean (Phaseolus vulgaris L.) to foliar applications of silver nanoparticles (GA-AgNPs 16.7 nm) and silver nitrate (AgNO3) each at 0.0, 5, 10, 20 and 60 ppm. The foliar application of GA-AgNPs and AgNO3 significantly increased plant height, root length, number of leaves/plant, the leaves' area, total fresh and dry weights/plant and yield (i.e., number, fresh and dry weights of pods/plant and 100-seed weight). It also altered protein patterns in the two varieties and changed the phytohormone balance in the Nebraska variety by increasing the levels of growth-regulating substances, which explains the increase in both growth parameters and yield in GA-AgNPs and AgNO3 treated plants. An Atomic Absorption Spectroscopy (AAS) study unveiled the movement and residual accumulation of both forms of silver in different parts of the two bean varieties. The results indicate the successful use of GA-AgNPs and AgNO3 in enhancing the growth and yield of the Bronco and Nebraska varieties under pot experiment conditions, and present a viable alternative to genetically modified (GM) crops for ensuring food security.