Ultrastructural leaf features of grapevine cultivars (Vitis vinifera L. ssp vinifera)

Aim: To investigate and compare Vitis vinifera Linne subsp. vinifera leaves of cultivars important for the Austrian wine producers in order to learn more about their surface architectures in the micro- and nanoscale. Methods and results: Atomic force microscopy, binocular fluorescence microscopy, contact angle measurements, and environmental scanning electron microscopy were employed in order to assess physicochemical features of fresh plant material. Erect and prostrate trichomes are the most characteristic features present on the epidermal surfaces of grapevine leaves. These hairs occur in rather different densities from none to densely covering the whole surface. Contact angles are highly affected by these hairs, resulting in individual cases in values > 150 degrees in the presence of a high reclining hair density. On nanoscopic scale, blades of the varieties differ with respect to their wax structures in orientation, shape and size. Cuticular striae and epicuticular waxes, mostly granules and platelets, are conspicuous characteristics of grapevine leaf ultrastructure. Conclusion: The microscopy techniques applied are complementary, enabling morphological analysis at different scales. They are not only efficient tools for descriptive botanics and for finding morphological adaptations to the environmental conditions, they provide also an insight into the habitat of leaf colonizing microbes, pathogenic as well as beneficial ones, and may add to the understanding of the conditions they find on leaf surfaces. Significance and impact of the study: Leaf surface structures and chemicals are part of the defence system of the plant. Water-repellency can be advantageous for the plant as it creates unfavourable conditions for the successful colonization of pathogens. The knowledge of wetting properties of leaf surfaces will advance the insight in the interaction with additives, promoting the secure and optimal use of plant protection agents applied by spray deposition, especially under difficult weather conditions. The application of such research will be better contact and/or penetration, better adhesion of pesticides and other plant protecting agents, and improved adhesion of plant promoting bacteria in biocontrol applications.