Viruses 2022, 14, 2151. https://doi.org/10.3390/v14102151 www.mdpi.com/journal/viruses Article Foliar Application of Nanoclay Promotes Potato (Solanum tu- berosum L.) Growth and Induces Systemic Resistance against Potato Virus Y Dalia G. Aseel 1, *, Ahmed Abdelkhalek 1, *, Fatimah O. Alotibi 2 , Marwa A. Samy 1 , Abdulaziz A. Al-Askar 2 , Amr A. Arishi 3 and Elsayed E. Hafez 1 1 Plant Protection and Biomolecular Diagnosis Department, Arid Lands Cultivation Research Institute, City of Scientific Research and Technological Applications, New Borg El Arab City 21934, Alexandria, Egypt 2 Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia 3 School of Molecular Sciences, The University of Western Australia, Perth, WA 6009, Australia * Correspondence: daliagamil52@gmail.com (D.G.A.); aabdelkhalek@srtacity.sci.eg (A.A.); Tel.: +20-1007556883 (A.A.) Abstract: Potato virus Y (PVY) is one of the most harmful phytopathogens. It causes big problems for potatoes and other important crops around the world. Nanoclays have been extensively studied for various biomedical applications. However, reports on their interactions with phytopathogens, particularly viral infections, are still limited. In this study, the protective activity of Egyptian nanoclay (CE) and standard nanoclay (CS) against PVY was evaluated on potato (Solanum tuberosum L.) plants. Their physicochemical and morphological properties were examined with scanning elec- tron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spec- troscopy (FTIR), and energy dispersive spectrometer (EDS). SEM and TEM analyses revealed that CE has a spherical and hexagonal structure ranging from 20 to 80 nm in size, while CS has boulder- like and tubular structures of about 320 nm in size. FTIR and EDS showed that both nanoclay types have different functional groups and contain many vital plant nutrients that are necessary for every stage and process of the plant, including development, productivity, and metabolism. Under green- house conditions, a 1% nanoclay foliar application enhanced potato growth, reduced disease symp- toms, and reduced PVY accumulation levels compared with non-treated plants. Significant in- creases in levels of antioxidant enzymes (PPO and POX) and considerable decreases in oxidative stress markers (MDA and H2O2) were also reported. Moreover, a significant increase in the tran- scriptional levels of defense-related genes (PAL-1, PR-5, and CHI-2) was observed. All experiment and analysis results indicate that the CE type is more effective than the CS type against PVY infec- tion. Based on these results, the foliar applications of nanoclay could be used to manage plant viral infections in a way that is both effective and environmentally friendly. To our knowledge, this is the first report of the antiviral activity of the foliar application of nanoclay against PVY infection. Keywords: Nanoclay; potato; PVY; FTIR; SEM; TEM, antioxidant enzymes; gene expressions 1. Introduction The potato (Solanum tuberosum L.) is a substantial and economical crop. Plant dis- eases are brought about by parasitic infections caused by oomycetes, microbes, viruses, parasitic plants, nematodes, or organisms and cause significant damage [1,2]. Plant phy- topathogens are responsible for 20 to 40% of annual output losses [3]. Furthermore, potato viruses usually damage the economy, hurting both the quality of the seeds and trade [4]. Potato virus Y (PVY) is potatoes’ major aphid-transmitted viral pathogen worldwide. It could impact the production of certified seeds and crops grown for processing or fresh Citation: Aseel, D.G.; Abdelkhalek, A.; Alotibi, F.O.; Samy, M.A.; Al-Askar, A.A.; Arishi, A.A.; Hafez, E.E. Foliar Application of Nanoclay Promotes Potato (Solanum tuberosum L.) Growth and Induces Systemic Resistance against Potato Virus Y. Viruses 2022, 14, 2151. https://doi.org/10.3390/v14102151 Academic Editor: K. Andrew White Received: 7 September 2022 Accepted: 27 September 2022 Published: 29 September 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).