Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Sustainability of pistachio production (Pistacia vera L.) under supplemental irrigation in a Mediterranean climate G. Marino a, ⁎ , S. Di Martino c , A. Amico Roxas b , T. Caruso c , L. Ferguson b , E. Barone c , F.P. Marra c a Department of Land Air and Water Resources, University of California, Davis, One Shields Ave., 95616 Davis, CA, USA b Department of Plant and Environment Sciences, University of California, Davis, One Shields Ave., 95616 Davis, CA, USA c Department of Agricultural, Food and Forest Sciences, University of Palermo, Viale delle Scienze Ed. 4, 90128 Palermo, Italy ARTICLE INFO Keywords: Stem water potential Gas exchange Yield Splitting Water savings Phenology ABSTRACT The objective of this study was to examine the effects of supplemental micro-irrigation, in a commercial rainfed orchard, on tree water status, gas exchange and productivity of Pistacia vera L. (cv Bianca) grafted on P. ter- ebinthus. Irrigating with 10–15% of estimated full evaporative demand significantly increased average annual productivity by increasing yield in the on-crop year of this alternate bearing species. Irrigation increased yield by 30%, resulting in 1600 kg of in-shell product per ha. Irrigation delayed leaf senescence while flower bud ab- scission was not reduced until the third year of experiment. Irrigation did not improve gas exchange during Stage I (pericarp growth). Both stomatal conductance (g s ) and maximum photosynthesis (A max ) increased with irri- gation during Stage III (intense embryo growth). Stem water potential appeared less sensitive than gas exchanges in detecting differences in water stress between treatments. The results suggest that the efficiency of irrigation can be improved taking into consideration crop load and tree phenology. The results also demonstrate pistachio production is environmentally and economically sustainable in Mediterranean areas having 500 mm rainfall, with as little as 100 mm of irrigation water. 1. Introduction Pistachio (Pistacia vera L.) is a drought resistant species (Behboudian et al., 1986; Rieger, 1995), native to Western Asia and Asia Minor (Ferguson, 1995). Due to its ability to survive and produce modest crops with little or no irrigation (Goldhamer, 1995) it was traditionally cultivated in arid regions on marginal soils. Multiple studies have defined the positive effect of irrigation on pistachio yield and quality (Goldhamer et al., 1985; Polito and Pinney, 1999; Goldhamer, 2005; Iniesta et al., 2008). More detailed studies have demonstrated irrigation’seffects on photosynthesis (De Palma and Novello, 1998), flower bud retention (Marra et al., 1998, 2009), and therefore the ability of irrigation to affect yield and alternate bearing (Kanber et al., 1993). As a result, if water is available, modern pro- duction orchards are irrigated. The most recent orchards developed with more vigorous, highly productive rootstocks and scions are es- tablished with the expectation of applying 1150 mm of irrigation per hectare annually and producing an average annual yield of 2500 kg per hectare of dried marketable in-shell split nuts (2015 Pistachio Costs & Returns Study). The studies above also demonstrated irrigated pistachio tree transpiration is much higher than that of other deciduous species. During the summer months, transpiration can peak at 8.1 mm d −1 (Iniesta et al., 2008; Goldhamer et al., 1985). The high volume irriga- tion regimes dictated by this high tree water use is not sustainable in most Mediterranean climates with their low water availability. This situation is particularly important as climate change decreases agri- cultural water supplies (Kiparsky and Gleick, 2003). Using Iran, for- merly the world’s largest producer and exporter, now second in both to California, as an example, many pistachio producing regions will either cease production or move due to lack of water (Financial Tribune, 2017). Pistachio’s differential responses to irrigation that suggests high volume irrigation may not be the best strategy for economic sustain- ability. Several authors reported that irrigation volumes meeting sea- sonal orchard evapotranspiration can be reduced by 50% in some phenological stages without affecting yield (Phene et al., 1987; Goldhamer and Beede, 2004; Gijón et al., 2009). Multiple studies have demonstrated a high variability of drought resistance (Phene et al., 1987; Goldhamer, 2005), water relations (Gijón et al., 2011) and photosynthetic performance (Marino et al., 2018a) depending on the phenological stage. It has been speculated these responses are a func- tion of tree maturity, variability, and cropping status (Obeso, 2002), https://doi.org/10.1016/j.scienta.2018.06.032 Received 9 March 2018; Received in revised form 3 June 2018; Accepted 13 June 2018 ⁎ Corresponding author. E-mail address: giumarino@ucdavis.edu (G. Marino). Scientia Horticulturae 241 (2018) 260–266 0304-4238/ © 2018 Elsevier B.V. All rights reserved. T