Biogenic extracellular synthesis of gold and silver nanoparticles by Trichoderma harzianum and Trichoderma longibrachiatum and their effectiveness against seed-borne fungal pathogens.

Nanoparticles present a multifunctional platform for a diverse range of applications in the modern agricultural concept of precision farming due to their small size, high surface to volume ratio and unique optical properties. Antimicrobial nano-materials, pathogen detection by the use of nano-sensors, spray-induced gene silencing (SIGS) are only some of the potentialities of the nanotechnology in crop protection. The biosynthesis of gold and silver nanoparticles (AuNPs and AgNPs) by Trichoderma harzianum and T. longibrachiatum was evaluated. Fungi were isolated from deep-sterilized tissues of Cupressus sempervirens and Gladiolus cv. ‘Red Balance’, respectively, and were molecularly identified using ITS and tef-1alfa sequences analyzed by TrichOKEY and TrichoBLAST. Cell-free extracts of the fungi were challenged with 1 mM silver nitrate and 0.5 mM tetracholoroauric acid solutions. The formed nanoparticles were characterized by means of spectroscopic and microscopic analyses including UV-VIS spectroscopy, TEM and XRD, EDAX and FT-IR analyses. Antifungal activity using a microdilution assay in 96-well microtiter plates against Colletotrichum lupini, Fusarium oxysporum f. sp. basilici and Botrytis cinerea was assessed. The results were transformed to percentage of controls and the IC50 and IC90 values were graphically obtained from the dose-response curves. The AgNPs of T. harzianum and T. longibrachiatum strongly reduced the growth rate of all tested pathogens (85-100%) and only the AuNPs of T. longibrachiatum gave rise to a reduction of growth between 18 and 56% depending on the pathogen tested. The promising results obtained open up opportunities for further research on effective and ecofriendly solutions for the control of seed-borne diseases.