Radiation Synthesis of Silver Nanoparticles/Chitosan for Controlling Leaf Fall Disease on Rubber Trees Causing by Corynespora cassiicola

Abstract

Silver nanoparticles (AgNPs) were successfully prepared by γ-rays irradiation of solution containing 1.0-10 mM of silver nitrate and 1% chitosan. The optical characteristics and particles sizes of AuNPs were determined by UV-Vis spectra and TEM images, respectively. The size of AgNPs increased by the increase of silver concentration or the decrease of chitosan molecular weight in irradiated solution. The in vitro test showed that AgNPs inhibited the growth of Corynespora cassiicola on rubber-leaf extract media with the inhibitory efficiency of 52.1-100% by treatment of AgNPs with particle size from 15 to 5 nm, respectively. In addition, antifungal activity was found to reach 100% by the addition of 90 ppm AgNPs. The in vivo foliar treatment of AgNPs on 9-month-old rubber plants showed that the treatment with 2.5-12.5 ppm AgNPs on tested plants after inoculation by spraying with C. cassiicola spores enhanced the rate of non-disease-infected plants from 6.0 to 93.3%, respectively, compared to the untreated control. The inhibition effect of AgNPs on fungal growth of C. cassiicola mycelial was also elucidated via SEM images. The AgNPs/chitosan synthesized by γ-irradiation is potentially promising to use as a fungicidal product for treating C. cassiicola, a serious pathogen fungus on rubber trees.