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Climate change scenarios and water restrictions are key challenges for Mediterranean citriculture, requiring sustainable deficit irrigation (DI) strategies to ensure sustainable yields. Further research on the physiological pathways that regulate crop responses to water stress is necessary. This work describes the physiological limitations induced under drought conditions in young Navelina orange trees, including the crop's capability to recuperate its physiological status upon rewatering and after water withholding. A trial was conducted in two-year-old trees subjected to three irrigation treatments: a full irrigation treatment (FI) and two different DI strategies. The results show significant decreases in gas exchange rates for stem water potential (ΨStem) values below −1.5 MPa, evidencing diffusive limitations from drought stress. Additionally, there was evidence of increased osmolyte synthesis, a preventative response to oxidative damage. Significantly increased levels of proline (Pro) and malondialdehyde (MDA) were observed with higher levels of water stress (ΨStem < −1.8 MPa), which leads us to assume that this threshold signals the presence of oxidative damage with no capacity for subsequent recovery, probably affecting the final yield. [ABSTRACT FROM AUTHOR]

Abstract: This study examines the suitability of trunk dendrometers for assessing fruit growth under deficit irrigation (DI) for two consecutive years in a mature citrus orchard. Two DI programmes were applied during the maximum evapotranspirative demand period: sustained-deficit irrigation, applied at 50% ETC on average, and low-frequency deficit irrigation, applied according to plant–water status, establishing different irrigation–restriction cycles. Additionally, a control treatment at 100% ETC was monitored for the entire irrigation season. Trunk daily growth (TDG) and fruit daily growth (FDG) were estimated together with stem-water potential at midday (Ψ stem) and the maximum daily shrinkage of the trunk (MDS). Significant relationships were determined for Ψ stem vs. TDG (R 2 =0.60), and vs. FDG (R 2 =0.78). In addition, significant relationships were established between TDG vs. FDG (R 2 =0.60), and between the daily increment of MDS (ΔMDS) and FDG (R 2 =0.50), revealing the strong connection between trunk and fruit variations caused by water stress. According to these findings, the DI effects on fruit growth can be monitored by means of TDF or temporal evolution of Ψ stem, promising automation possibilities for appropriately regulating irrigation under DI programmes, and predicting its effects on fruit size by continuous field measurement. [Copyright &y& Elsevier]

Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orange orchard (Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experiment consisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration (ETc) values for the whole season, and three SDIs imposed as a function of different water-stress index (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. The values defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured through the midday stem-water potential (ΨStem). Yearly, yield and fruit quality were evaluated at harvest in each treatment, and a global analysis was carried out using the whole dataset. Overall, no significant differences were found in fruit yield between SDIs and control treatments, although significant differences appeared in some of the fruit-quality parameters (total soluble solids and titrable acidity) which also showed significant relationships with integrated stem-water potential (ΨInt ) and irrigation water applied. These findings lead us to conclude that SDIs have important and statistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDI with WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the water productivity for citrus orchards in a semiarid Mediterranean climate. [ABSTRACT FROM AUTHOR]

Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orange orchard (Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experiment consisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration (ETc) values for the whole season, and three SDIs imposed as a function of different water-stress index (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. The values defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured through the midday stem-water potential (ΨStem). Yearly, yield and fruit quality were evaluated at harvest in each treatment, and a global analysis was carried out using the whole dataset. Overall, no significant differences were found in fruit yield between SDIs and control treatments, although significant differences appeared in some of the fruit-quality parameters (total soluble solids and titrable acidity) which also showed significant relationships with integrated stem-water potential (ΨInt) and irrigation water applied. These findings lead us to conclude that SDIs have important and statistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDI with WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the water productivity for citrus orchards in a semiarid Mediterranean climate. [ABSTRACT FROM AUTHOR]