agronomy Review Drought and Salinity in Citriculture: Optimal Practices to Alleviate Salinity and Water Stress Vasileios Ziogas 1, *, Georgia Tanou 2 , Giasemi Morianou 1 and Nektarios Kourgialas 1, *   Citation: Ziogas, V.; Tanou, G.; Morianou, G.; Kourgialas, N. Drought and Salinity in Citriculture: Optimal Practices to Alleviate Salinity and Water Stress. Agronomy 2021, 11, 1283. https://doi.org/10.3390/ agronomy11071283 Academic Editor: Susanna Bartolini Received: 14 May 2021 Accepted: 22 June 2021 Published: 24 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Institute of Olive Tree Subtropical Crops and Viticulture, ELGO—DIMITRA, 73134 Chania, Greece; morianou@elgo.iosv.gr 2 Institute of Soil and Water Resources, ELGO—DIMITRA, Thermi, 57001 Thessaloniki, Greece; gtanou@swri.gr * Correspondence: ziogas@elgo.iosv.gr (V.Z.); kourgialas@elgo.iosv.gr (N.K.) Abstract: Among the various abiotic stresses, drought is the major factor limiting crop productivity worldwide. Citrus has been recognized as a fruit tree crop group of great importance to the global agricultural sector since there are 140 citrus-producing countries worldwide. The majority of citrus- producing areas are subjected to dry and hot summer weather, limited availability of water resources with parallel low-quality irrigation water due to increased salinity regimes. Citrus trees are generally classified as “salt-intolerant” with high water needs, especially during summer. Water scarcity negatively affects plant growth and impairs cell metabolism, affecting the overall tree growth and the quality of produced fruit. Key factors that overall attempt to sustain and withstand the negative effect of salinity and drought stress are the extensive use of rootstocks in citriculture as well as the appropriate agronomical and irrigation practices applied. This review paper emphasizes and summarizes the crucial role of the above factors in the sustainability of citriculture. Keywords: abiotic stresses; citrus water needs; irrigation practices; sustainability of citriculture 1. Introduction Citrus has been recognized as a group of fruit tree crops of great importance for the global agricultural sector. The majority of the cultivated areas of citrus are located in the subtropical region, in the so-called citrus belt, defined by the 40 ◦ north–south latitudes, where the temperature rarely drops below severe freezing temperatures [1]. The majority of the citrus-producing areas are subjected to dry and hot summer weather, limited availability of water resources with parallel low-quality irrigation water due to increased salinity regimes. These factors negatively affect citrus tree productivity and fruit quality. Furthermore, the negative effect of climate change in citrus-producing areas should not be neglected since it augments the detrimental effect of salinity and drought stress [2]. Climate change, combined with the resulting desertification and overexploitation of water resources, due to overpopulation and intensification of agriculture, will be a challenge for the survival, growth, and sufficient yield of agricultural commodities [3]. Especially in citrus crops, water scarcity negatively affects plant growth and impairs cell metabolism, affecting the overall tree growth and produced fruit quality. Drought stress is also affecting the post-harvest handling of citrus fruit since it reduces significantly the reed thickness, rendering the fruit more prone to damage during handling and transportation [4]. Salinity and drought stress demonstrate similar physiological disorders to plants when they occur. Under the effect of salinity and drought stress, interlinked molecular responses are activated in order to provide an acclimation effect to the plant and initiate signaling cascades so as to facilitate the alleviation of the occurred stress syndromes [5]. There are several molecular interactions between salinity and drought stress that are impossible to separate in the field. Additionally, overall plant responses to simultaneous stress factors are complex and can be different in terms of response to each individual stress factor, depending also upon the duration and intensity of each stress syndrome [2]. Agronomy 2021, 11, 1283. https://doi.org/10.3390/agronomy11071283 https://www.mdpi.com/journal/agronomy