Light and electron microscopy techniques for plant health support

Plants play a key role for the planet, as they support ecosystems, regulate the climate and provide essential resources for all living organisms. One of the main threats to plant health is plant pests, and a vast variety of new technologies, including imaging techniques, are useful tools for addressing this issue. This doctoral thesis primarily focuses on the potential applications of imaging techniques, particularly light and electron microscopy, in various fields related to plant health. Specifically, the research activity carried out explored the use of these tools to investigate the morpho-functional characteristics of plant pests, to report and discuss their associations with other organisms, and to evaluate the effectiveness and related effects of potential plant pest control strategies. Chapter 1 provides an overview of plant health, its global relevance and the impact of plant pests, as well as possible control strategies. It also outlines the applications of light and electron microscopy in plant health. Chapter 2 investigates a previously unreported recurrent association between the nematode Rhabditis (Rhabditella) axei (Chitwood, 1933) and the invasive palm borer Paysandisia archon (Burmeister, 1880). Light and scanning electron microscopy were used to perform morphological and morphometric analyses of the nematode. Chapter 3 focuses on the ultrastructure of spermiogenesis in the brown marmorated stink bug Halyomorpha halys (Stål, 1855), investigated by transmission electron microscopy and fluorescence microscopy. Wild-type and X-irradiated males were compared, within the framework of the application of the Sterile Insect Technique, in order to investigate potential alterations in spermiogenesis associated with X-ray exposure. Chapter 4 deals with the development of a new nanoformulation of the systemic pesticide Fosetyl-Al coated with chitosan. The resulting Chitosan-based Fosetyl-Al nanocrystals (CH-nanoFos) were characterised using transmission electron microscopy and infrared spectroscopy, and then tested for its potential efficacy in controlling the plant-parasitic nematode Meloidogyne javanica (Chitwood, 1949), using in vitro and pot experiments. The physiological and cytogenetic effects of CH-nanoFos were assessed on Solanum lycopersicum (Linnaeus, 1753) cv. Cuore di Bue seedlings and plants. Additionally, the uptake of CH-nanoFos by tomato seeds and plants, and the related modification of the biomolecular landscape, were evaluated using transmission electron microscopy and infrared spectroscopy. Finally, a critical summary of the microscopy techniques employed in this thesis is provided, highlighting their main strengths and limitations. This comparative analysis enables a discussion of the contribution and applicability of each approach in the study of plant health and associated organisms.