Ecology, Environment and Conservation Paper

EVALUATION OF EFFICACY OF COLLOIDAL SILVER PARTICLESAGAINST LATE BLIGHT OF POTATO (PHYTOPHTHORA INFESTANSL.)

Shantamma, K.T. Rangaswamy, N. B. Prakash and Raghavendra Achari

Abstract

Colloidal silver was synthesized by the ‘bottom up’ approach of wet chemical method and analyzed bylaser Dynamic Light Scattering (DLS). The colloidal silver solution synthesized was having a particle sizewith a mean diameter of 149.4 nm. Tested the efficacy of synthesized colloidal silver particles under in vitroconditions (10 ppm, 25 ppm, 50 ppm,100 ppm 250 ppm and 500 ppm) against Phytophthora infestans. Amongthe different concentrations maximum inhibition of mycelial growth was recorded at higher concentrations(250 ppm and 500 ppm). To know the further effectiveness of higher concentrations of colloidal silverparticles were tested alone (250 ppm and 500 ppm) and in combination with fungicides (Cymoxanil 8 % +mancozeb 64 % WP@ 0.2 % and Dimethomorph @ 0.2%) under field conditions. The spray solutions ofcolloidal silver at 500 ppm recorded significantly less late blight disease severity at 90 days after sowing(DAS) (42.22 PDI) when compared to @ 250 ppm (60.74 PDI) and untreated plants (75.56 PDI). The foliarapplication of colloidal silver @ 500 ppm is found on par with Cymoxanil 8 % + mancozeb 64 % WP@ 0.2% whereas superior over Dimethomorph 50% WP @ 0.2%. Further, colloidal silver both @ 250 ppm and 500ppm when used in combination with fungicides could not significantly complemented the efficacy offungicides viz., Cymoxanil 8 % + Mancozeb 64 % WP @ 0.2 % and Dimethomorph 50% WP @ 0.2% inreducing the late blight disease severity at 90 DAS, but recorded significantly less disease severity thanuntreated control plants. Examined the biochemical response of plant defense mechanism pertaining todefense related enzymesin treated and untreated plants. The increased activity of peroxidase (PO) (1.5mg/g), polyphenol oxidases (PPO) (0.01 mg/g) and phenylalanine ammonia lyase PAL (1.5 mg/g) wasobserved in late blight infected potato plants treated with colloidal silver particles @ 500ppm and incombination of 0.2 per cent of Cymoxanil 8 % + Mancozeb 64 % WP fungicide.