Study of the biological activity of arabinogalactan-stabilized silver nanoparticles towards watercress Lepidium sativum L. Curled and plant pathogenic micromycete Fusarium sambucinum

Metal nanoparticles (NPs) exhibiting growth-stimulating, antifungal, antibacterial, insecticidal effects and prolonged release of minerals and herbicides, opens up prospects for increasing the yield of crops. Among metal nanoparticles that can find application in agriculture, silver nanoparticles occupy a special place due to a wide spectrum of biological activity. In this work, we have established for the first time that the pre-sowing treatment of seeds of watercress Lepidium sativum L. cv. Curled by silver nanoparticles which are stabilized by the biopolymer arabinogalactan and dioctyl sulfosuccinate affects the germinative energy, laboratory seed germination and some anatomical and morphometric parameters of watercress seedlings. It was shown for the first time that silver nanoparticles have an inhibitory effect on the growth of the phytopathogenic fungus Fusarium sambucinum . This work aimed to assess both the stimulating effect of silver nanoparticles (Ag-NPs) stabilized with arabinogalactan and dioctyl sulfosuccinate on growth of watercress Lepidium sativum L. cv. Curled seedlings and the antifungal effect on a plant pathogenic toxin-producing micromycete Fusarium sambucinum VKPM F-900. The nanoparticles were synthesized by the reduction of silver nitrate in an alkaline medium in the presence of arabinogalactan followed by the addition of dioctyl sulfosuccinate as a stabilizer. The average nanoparticle diameter was 11.40±3.96 nm; zeta potential -24 mV. The effect of silver nanoparticles on germination energy, seed germination, growth of watercress seedling hypocotyl and root was investigated. Seeds were incubated in sols of nanoparticles with various silver concentrations (1.17, 2.34, 4.69, 9.38, 18.75. 37.5, 75, and 150 mg/ml). Control seeds were incubated in water. After incubation, the seeds were germinated in Petri dishes on a wet bed of filter paper in the dark at 20 °С. The seed germination energy was determined on day 3, the laboratory germination - on day 5, the lengths of the hypocotyl and the main root were measured on day 7, and also microscopic analysis of the root sections of seedling treated with sols with stimulating and inhibiting concentrations of Ag (4.69 and 18.75 mg/ml, respectively) was carried out. Antifungal activity of silver sols with concentrations from 9.38 to 300 mg/ml was assessed by the agar diffusion method. Micromycete Fusarium sambucinum Fuckel VKPM F-900 was used as a test culture to determine antifungal activity. Sterile water was used as a control. The incubation of seeds in sols with a silver concentration of 2.34 and 4.69 mg/ml had a stimulating effect on the germination energy and laboratory germination of L. sativum seeds. A dose of silver nanoparticles of 4.69 mg/ml increased the germination energy by 13.5 % and laboratory germination by 11.7 % compared to the control. In addition, the concentrations of silver from 1.17 to 4.69 mg/ml had a significant stimulating effect on root growth (from 34.4 to 79.1 %, respectively) with some deceleration of hypocotyl growth. Seed incubation in sols with a silver concentration of 18.75 mg/ml and higher led to a significant decrease in the germination energy and laboratory germination, as well as suppression of plant growth. Microscopic examination of sections of zone of maturation of the root of seedlings showed that silver sols significantly affect the conductive system of the central axial cylinder. The number of xylem vessels in seedlings treated with silver sol at a stimulating concentration of 4.69 mg/ml was significantly higher compared to the control, which led to a more intensive growth of the root system and the whole plant. Silver nanoparticles also inhibit the growth of F. sambucinum . The growth inhibition zone at a maximum sol concentration of 300 mg/ml was 32.4±4.2 mm in diameter, and at 150 mg/ml it was 28.4±3.9 mm. The minimum concentration inhibiting the visible growth of the test strain F. sambucinum was 18.75 mg/ml (growth inhibition zone 11.7±0.8 mm). The presented data indicate the possibility of using sols of stabilized silver nanoparticles to stimulate seed germination and plant growth and to protect plants against pathogens.