Adjustement of water use efficiency by stomatal regulation during drought and recovery of Verona province grape varieties grafted on two different Vitis hybrid rootstocks.

Drought is considered to be the predominant factor both for determining the geographic distribution of vegetation and for restricting crop yields in agriculture. Furthermore, water stress is a limiting factor for a wide range of plant physiological processes and can have a profound effect on plant metabolism and development. Drought stress can decrease the sensitivity of photosynthesis to subsequent water deficits and similarly reduce the sensitivity of stomata to low atmospheric vapor pressure deficit during the dry season. Grapevine cultivars are known to differ in their drought adaptation mechanisms, but there is little knowledge on how many of them behave during a drought event and after recovering. The aim of this study is to analyze how stomatal conductance is regulated under water stress and recovery, as well as how water stress affects adjustments of water use efficiency in cultivar Corvina, Corvinone and Rondinella grafted on Kober 5BB and 140 Ruggeri rootstocks. The experiment was conducted on 4-year old vines, grown in an experimental field of Valpolicella in Verona province. The effects of water deficit and recovery after rewatering were evaluated by using thermal imaging, a potential tool for estimating plant temperature, which can be used as an indicator of stomatal closure and water deficit stress. The thermal indices were compared with measured stomatal conductance. Results of mid-morning and at noon measurements showed significant difference between cultivars for both stomatal conductance and canopy water stress index. An apparent difference between the cultivars was the highest speed of the recovery noted for Corvinone compared to Corvina and Rondinella. The possible relation between water use differences and production and quality of grapes at harvest are discussed.