Leaf thickness and structure of <em>Vitis vinifera</em> L. cv. Albariño clones and its possible relation with susceptibility to downy mildew (<em>Plasmopara viticola</em>) infection

Abstract

<p style="text-align: justify;"><strong>Aims</strong>: The grapevine (<em>Vitis vinifera</em> L.) cultivar Albariño is currently the most economically important in Galicia (northwestern Spain). Earlier works assessing the natural susceptibility to downy mildew leaf infection (both in the laboratory and in the field), carried out in the collection of Albariño clones at the Misión Biológica de Galicia (CSIC), showed great differences among the clones (Boso <em>et al.</em>, 2004b, 2005b, 2006; Boso and Kassemeyer, 2008). The aim of the present work is to highlight the histological differences in leaves, in particular thickness and structure, among the 11 different Albariño clones and to find out their possible relation with their natural susceptibility to <em>Plasmopara viticola</em>.</p><p style="text-align: justify;"><strong>Methods and Results</strong>: Transverse sections of adult leaves where prepared and observed under light microscope. The area corresponding to the different leaf layers was measured. The results showed significant differences between the clones regarding the thickness of the spongy mesophyll. The clones CSIC-4 and CSIC-1 had the thickest spongy mesophyll (average mean = 14316.8 μm<sup>2</sup>) whereas CSIC-3 showed the thinnest one (11548.1 μm<sup>2</sup>).</p><p style="text-align: justify;"><strong>Conclusion</strong>: The CSIC-3 clone, one of the least susceptible clones to <em>P. viticola</em> in previous studies, showed the thinnest and most compact spongy mesophyll. On the contrary, the CSIC-1 clone had the thickest spongy mesophyll and was also one of the most susceptible to this pathogen. Therefore, it could be possible to relate their histological leaf characteristics with their different levels of natural susceptibility to <em>P. viticola</em>.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This work contributes to the understanding of the link between histological characteristics of leaf layers and mesophyll cells and the different natural susceptibility of grapevines to downy mildew. This may become in the future a valid tool to be used during clonal selections in grapevine breeding programs.</p>