**3.3. Peach**

For peach, the use of Ψstem for defining thresholds under DI conditions is referred by Girona et al. [70], who found the value −1.5 MPa, the limit over which the impairing of bloom fertility appears. Naor et al. [39] have observed that the value of −2.0 MPa for SWP was a threshold for the occurrence of double fruits, while Lopez et al. [71] suggest a threshold of −1.05 MPa to obtain fruits with positive effects on consumer acceptance, without significant impacts on fruit composition and yield, as they have observed that a threshold of −1.25 MPa would reduce fruit size and yield, even if advantageous for consumer acceptance.

Other authors, using relative transpiration (RT), have observed that a minimum value of 0.7 has to be observed to avoid yield and quality losses [72].

Using the relationship between (RT) and Ψpd, it was observed [73] that the Ψpd threshold corresponding to RT equal to 0.7 is −0.33 MPa. Using CWSI, based on the temperature differences between canopy and air, a threshold of 0.5 was found to trigger irrigation [74]. It was also found that it is possible to identify a threshold in the relationship between gs and Ψp, corresponding to a change in the plant behavior, equal to Ψpd = −0.45 MPa [75].

information is quite complex and scattered. Classical recommendations often include the use of leaf water potential [94]; a new water stress index based on a water balance model was proposed and tested by Gaudin et al. [95] as a tool for classifying water stress experienced by

Deficit Irrigation in Mediterranean Fruit Trees and Grapevines: Water Stress Indicators and Crop…

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Shoots growth and fruits development are cyclical and both are repeated on an annual basis, but only vegetative growth is completed in the same year, while olives production needs two consecutive seasons [96]. In the first one, the formation of the buds and their floral induction take place. In the following year, flower development occurs as well as flowering, fruit set, growth, and oil accumulation. In Mediterranean climate conditions of northern hemisphere, shoot growth takes place from March until the middle of July, although a second flow of growth can occur in late August, when olive trees are fully irrigated, or at the beginning of autumn rainfall [97]. Water deficit reduces shoots growth and has a negative effect on the potential production of the following year. Flowering occurs at the end of spring, and it is very sensitive to water deficit [63], or at high temperatures. Fruit set is very sensitive to water deficit and fruit growth has a double sigmoid behavior [96, 98] with three main stages, as follows. Phase I is the fast-growing, when both the cell division and expansion contribute to the size increase, the endocarp being the main tissue in development, reaching 80% of the volume of the olives [98] with full expansion about 8 weeks after full bloom [99]. The occurrence of water deficit in this stage results in a small endocarp and extreme water stress can compromise the viability of the fruit. Phase II, of slow-growth, is less sensitive to water deficit [100], when the endocarp progressively hardens and both the embryo and the endocarp reach their final size [98]. During phase III, of fast growing, parenchyma cells of the mesocarp experience a large increase in size, entirely due to cell expansion, and the oil biosynthesis begins [98]; so water availability for the fruit determines its size and the accumulation of oil. Thus, water deficit may produce small fruits and the mesocarp/endocarp ratio is reduced due to decreased weight of the mesocarp.

Many studies had showed that high soil water availability increments yield components such as fruit number, fruit fresh weight, fruit volume, pulp:stone ratio, and oil content; therefore, increasing fruit and oil yields [12, 63] and that water scarcity can have a negative effect, depending on its level. In addition, irrigation regime can influence the relationship between

Hernandez-Santana [102] observed that olive trees prioritize fruit growth and oil content accumulation over vegetative growth, suggesting a higher sink strength for reproductive growth

**4. Responses to deficit irrigation regarding agronomic aspects and** 

grapevines in vineyards.

*4.1.1. Vegetative growth and production cycle*

*4.1.2. Olive response to water deficit*

vegetative and reproductive growth [101].

**quality**

**4.1. Olive**
