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Abstract In this work we compare the antifungal capacity of zinc oxide nanoparticles (ZnO-NPs) synthesized by a chemical route and a ZnO-based nanobiohybrid obtained by green synthesis in an extract of garlic (Allium sativum). To find out the characteristics of the materials synthesized, X-ray diffraction (XRD), IR spectroscopy and absorption in UV–Vis were used, as well as both scanning (SEM) and transmission (TEM) electron microscopy. The results showed that the samples obtained were of nanometric size (<100 nm), with a predominance of the wurtzite crystal phase of ZnO and little crystallization of the nanobiohybrids. Their antifungal capacity on two pathogenic fungi of coffee, Mycena citricolor (Berk and Curt) and Colletotrichum sp. was also evaluated. Both nanomaterials showed an efficient antifungal capacity, particularly the nanobiohybrids, with ~97% inhibition in growth of M. citricolor , and ~93% for Colletotrichum sp. The microstructural study with high resolution optical (HROM) and ultra-structural microscopy (using TEM) carried out on the fungi treated with the synthesized nanomaterials showed a strong nanofungicidal effect on the vegetative and reproductive structures and fungal cell wall, respectively. The inhibition of the growth of the fungi and micro and ultra-structural affectations were explained considering that the size of the nanomaterials allows them to pass easily through the cell membranes. This indicates that they can be absorbed easily by the fungi tested here, causing cellular dysfunction. Nanofungicide effects are also attributable to the unique properties of nanomaterials, such as the high surface-to-bulk ratio of atoms and their surface physicochemical characteristics that could directly or indirectly produce reactive oxygen species (ROS), which affect the proteins of the cell wall. Graphical abstract Unlabelled Image Highlights • ZnO-based nanomaterials were synthesized and characterized. • Nanomaterial antifungal activities over fungi that affect coffee were evaluated. • Micro and ultra-structural effects from ZnO-nanofungicides on the fungi were analyzed. • The treatment antifungal with Zn nano-biohybrids were most effective. [ABSTRACT FROM AUTHOR]

Coffee cultivation around the world is affected by phytopathogenic fungi, among them Colletotrichum sp., the causative agent of anthracnose. In the present work, therefore, an in vitro study was carried out on the antifungal effect of zinc oxide nanoparticles (ZnO-NPs) obtained by a chemical route on Colletotrichum sp. To this end, the area of growth of the fungus exposed to the action of concentrations of 9 mmolL−1 (730 ppm), 12 mmolL−1 (980 ppm), and 15 mmolL−1 (1200 ppm) of ZnO-NPs was monitored and their behavior was compared with the effect of the fungicide, ciproconazole (positive control) as well as with a sample of the fungus that grew normally (negative control). The ZnO-NPs showed an appreciable percent inhibition of fungal growth, ~96% for the concentration of 15 mmolL−1 at 6 days, causing loss in the continuity of some hyphae and the formation of groups of hyphal structures. Additionally, the ZnO-NPs favored the formation of structures of compact appearance (similar to vacuoles) within the hypha, as well as decreasing the cytoplasmic space. Image 1 • The antifungal activity of ZnO nanoparticles on Colletotrichum spp. was evaluated. • The micro and ultrastructural effects of the ZnO-NPs over fungi were analized. • The evaluated ZnO-NPs significantly inhibited the growth of the Colletotrichum spp. • The synthesized ZnO nanoparticles could potentially be used to protect coffee crops. [ABSTRACT FROM AUTHOR]