Water saving under drought stress is assured by stomatal closure driven by active (ABA-mediated) and/or passive (hydraulic-mediated) mechanisms. There is currently no comprehensive model nor any general consensus about the actual contribution and relative importance of each of the above factors in modulating stomatal closure in planta. In the present study, we assessed the contribution of passive (hydraulic) vs active (ABA mediated) mechanisms of stomatal closure in V. vinifera plants facing drought stress. Leaf gas exchange decreased progressively to zero during drought, and embolism-induced loss of hydraulic conductance in petioles peaked to ~50% in correspondence with strong daily limitation of stomatal conductance. Foliar ABA significantly increased only after complete stomatal closure had already occurred. Rewatering plants after complete stomatal closure and after foliar ABA reached maximum values did not induced stomatal re-opening, despite embolism recovery and water potential rise. Our data suggest that in grapevine stomatal conductance is primarily regulated by passive hydraulic mechanisms. Foliar ABA apparently limits leaf gas exchange over long-term, also preventing recovery of stomatal aperture upon rewatering, suggesting the occurrence of a mechanism of long-term down-regulation of transpiration to favor embolism repair and preserve water under conditions of fluctuating water availability and repeated drought events.

The self-incompatibility type is of key importance to understanding pollination in orchards, because most olive cultivars are partially self-incompatible and thus require pollinizers to ensure fruit set. The gametophytic model has been advocated to function in the olive, but no allele pair has been attributed to any variety. The GSI model failed in most combinations to explain fruit set. Olive growers must screen experimentally and empirically to look for inter-compatible pair-wise combinations of varieties for optimum pollination. The sporophytic model, with given dominance relationships for six S-alleles matches 98 % of the experimental data of the two sets investigated. We propose a method to analyze data from controlled crosses between olive cultivars applied to two experiments for varieties crossed in a diallel design. Furthermore, the dominance between the S-allele pair allows rational prediction of olive variety self-incompatibility levels. The S-allele pairs were unraveled for more than 60 cultivars. To go further, crosses between reference varieties-those in which the S-allele pair was unraveled-and varieties under experimentation (VarE) with an unknown S-allele pair will enable an increase in knowledge and the choice of the best pollinizers in silico. Nevertheless, we pose outstanding questions in orchards where open-pollination efficiency with varieties harboring the R2R3, R1R3, R1R5, or R3R5 pairs. These S-allele pairs require pollen grains without R2 or R3 , R1 or R3, and R3 or R5 determinants. Such pollinizer varieties are not abundant in France and Italy, and this questions whether their spread is sufficient for optimal pollination of main varieties

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Current understanding of physiological mechanisms governing stomatal behavior under water stress conditions is still incomplete and controversial. It has been proposed that coordination of stomatal kinetics with xylem vulnerability to cavitation [vulnerability curve (VC)] leads to different levels of isohydry/anisohydry in different plant species/cultivars. In this study, this hypothesis is tested in Vitis vinifera cultivars displaying contrasting stomatal behavior under drought stress. The cv Montepulciano (MP, near-isohydric) and Sangiovese (SG, anisohydric) were compared in terms of stomatal response to leaf and stem water potential, as possibly correlated to different petiole hydraulic conductivity (k(petiole)) and VC, as well as to leaf water relations parameters. MP leaves showed almost complete stomatal closure at higher leaf and stem water potentials than SG leaves. Moreover, MP petioles had higher maximum k(petiole) and were more vulnerable to cavitation than SG. Water potential at the turgor loss point was higher in MP than in SG. In SG, the percentage reduction of stomatal conductance (PLg(s)) under water stress was almost linearly correlated with corresponding percentage loss of k(petiole) (PLC), while in MP PLg(s) was less influenced by PLC. Our results suggest that V. vinifera near-isohydric and anisohydric genotypes differ in terms of xylem vulnerability to cavitation as well as in terms of k(petiole) and that the coordination of these traits leads to their different stomatal responses under water stress conditions.

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