Aims:The aim of this paper is to evaluate the photoinhibition capability, CO2 fixation activity and some adaptive mechanisms external to the photosystem II reaction centres in Sangiovese grapevine subjected to drought conditions. Methods and results:The diurnal time courses of gas-exchange and chlorophyll fluorescence parameters were monitored on free (natural position) and artificially retained (horizontal) leaves in Sangiovese potted vines maintained at 90 % and 40 % of maximum water availability from fruit-set to veraison. Changes in leaf and shoots characteristics were also monitored. Under drought, the inhibition of photosystem II in Sangiovese leaves may be severe and persistent according to leaf position (basal leaves with chlorosis and necrosis) and ability to avoid direct light (medial leaves with a more vertical position followed by lower temperatures and higher CO2 fixation capability and water use efficiency during the hottest hours of the day). Conclusion:In the Sangiovese leaves developed under drought, the protective effect of increasing leaf angle with a more vertical position and the energy costs saved by reducing photosynthetic pigments formation, changing leaf optical properties, diminishing xylem and shoot growth and leaf area development and limiting down-regulation of photoassimilation help maintain high physiological efficiency in all the distal leaves. Significance and impact of study:The results indicate that cultivar Sangiovese exhibit high adaptation to dry conditions. Key words: leaf orientation, chlorophyll fluorescence, net photosynthesis, stomatal conductance, photosynthetic pigments Objectif : L'objectif de cette recherche est d'évaluer, chez le cépage Sangiovese, la capacité de photo-inhibition, l'activité de fixation du CO2 et certains mécanismes extérieurs aux centres réactionnels du PSII en conditions de sécheresse. Conclusion : Chez les feuilles de Sangiovese qui se sont développées en conditions de sécheresse, l'effet de protection obtenu en augmentant l'angle des feuilles les plus verticales et, par ailleurs, les économies d'énergie découlant de différents facteurs (diminution de la formation de pigments photosynthétiques, modification des propriétés optiques de la feuille, diminution de la croissance du xylème et des pousses, limitation de la régulation négative de photoassimilation) aident à maintenir à un niveau élevé l'efficience physiologique des feuilles distales. Méthodes et résultats Signification et impact de l'étude

As in any other plant, the grapevine roots play a vital role in terms of anchorage, uptake of water and nutrients, as well as storage and production of chemicals. Their behaviour and development depend on various factors, namely rootstock genetics, soil physical and chemical features, and field agronomic practices. Canopy management, involving techniques such as defoliation and pruning, could greatly influence root growth. To date, most of the studies on grapevine winter pruning have focused on the effects on yield and quality of the grapes achievable through different pruning systems and techniques, while knowledge regarding root distribution, development, and growth in relation to winter pruning is still not completely understood. In this context, the purpose of our study was to investigate the effect of winter pruning on the root system of field-grown Vitis vinifera cv. Pinot Gris grafted onto rootstock SO4. We compared two pruning treatments (pruned-P and no pruned-NP) and analysed the effect on root distribution and density, the root index, and the root sugar reserve. Root data were analysed in relation to canopy growth and yield, to elucidate the effect of winter pruning on the root/yield ratio. Our data indicated that: (1) winter pruning stimulated the root growth and distribution; (2) canopy development was not negatively affected by this technique; (3) no pruned treatment produced less growth of the roots but a larger canopy. Information regarding both root growth and root canopy ratio is important as it gives us an understanding of the relationship between the aerial and subterranean parts of the plant, how they compete, and finally, offers us the possibility to ponder on the cultural practices.

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Hailstorms are typically localized events, and very little is known about their effect on crops. The objective of this study was to examine the physiological and vine performance responses to natural hail, registered four weeks after full bloom, of field-grown Thompson seedless (Vitis vinifera L.) grapevines, one of the most important table grape varieties cultivated in Greece and especially in the Corinthian region in northeastern Peloponnese. Leaf gas exchange, vegetative growth, vine balance indices, cane wood reserves, yield components, and fruit chemical composition were recorded from hail-damaged vines and compared with control vines. Visibly, the extent of the hailstorm damage was great enough to injure or remove leaves as well as cause partial stem bruising and partial injury or total cracking of berries. Our results indicated that natural hail did not affect leaf photosynthesis, berry weight, total acidity, and cane wood reserves but significantly reduced the total leaf area, yield, and the total phenolics of berries at harvest. At the same time, hail-damaged vines increased the leaf area of lateral canes and presented a higher total soluble solid (TSS) accumulation, while no effect on the next year’s fertility was registered. The present work is the first attempt to enhance our understanding of the vegetative yield, berry quality, and physiological responses of grapevines to natural hail, which is an extreme and complex natural phenomenon that is likely to increase due to climate change.