Physiological Influence of Water Stress Conditions on Novel HLB-Tolerant Citrus Rootstocks

Citrus are one of the most relevant fruit crops in the Mediterranean basin, which is the second-highest citrus-growing region in the world. However, these crops are mainly grown under Mediterranean semi-arid conditions, characterized by long periods of drought and torrential rain. In this work, we have assessed the response of three promising HLB-tolerant citrus rootstocks (Orange-14, UFR-1, and B11R3T27) to the application of four water stress conditions (Control, Mild water stress, Drought, and Flooding), comparing them with Carrizo citrange. Aerial plant symptoms were recorded during the experimental period, whereas plant water parameters, including stomatal conductance, leaf water potential, and relative water content, were obtained at the end of the assay. For all assessed rootstocks and variables, drought treatment was the most limiting factor, with Carrizo citrange being the most suitable rootstock under this condition. Flooding was the second restrictive treatment, in which UFR-1 was the least affected rootstock. Mid-water stress with 50% water requirements did not differ from the Control treatment, which can help save water resources in semi-arid regions. This information can be helpful for the citrus industry to increase the efficiency of citrus crops subject to water stress in semi-arid regions.