EFFECT OF DEFICIT IRRIGATION ON WATER STATUS, METABOLIC CHARACTERS, FRUITING, YIELD, AND QUALITY OF CLEMENTINE TREES UNDER TUNISIAN SEMI-ARID CONDITIONS

Water scarcity is one of the most serious threats facing humanity, and it is primordial to adopt water-saving strategies to improve irrigation efficiency in agriculture. The current study sought to determine the impact of a partial root-zone drying technique (PRD) used during fruit growth phases II and III (50% of crop water requirement) on water status, yield, and metabolic and technological characteristics of Citrus clementine MA3 during two consecutive seasons (2016-2017 and 2017-2018) under a Mediterranean semi-arid climate. The results of this research revealed that compared to control irrigation, the partial root drying irrigation system decreased the leaf water potential (psi l) by 35.9% and 12.9%, the leaf water content by 5.2% and 3.2%, and the chlorophyll index by 8.3% and 4.3%, but increased leaf temperature by 2.3% and 3.2%, leaf sugar content by 6.5% and 7.1%, proline content by 8.4% and 18%, and membrane permeability by 6.4% and 7.5%, respectively, in fruit growth stages II and III. The reaction of clementine trees to the application of PRD appeared clearly in the second year by reducing the fruit size by 7.1% and 7.3%, respectively, in phases II and III of fruit growth. PRD did not affect fruit number or yield in the first year but reduced them by 18% and 16% in the second year, respectively. PH was affected by the partial root drying and showed an increase of 0.9% in the second year of the experiment. Fruit weight, TSS, total sugar content, titratable acidity, and maturity index were maintained under partial root drying. Although the non-significant effect of PRD on quality attributes increased slightly, the TSS by 1.7 %, the total sugar content by 1.8 %, the maturity index by 2.5 %, and titratable acidity by 0.6 %. Despite the decrease in chlorophyll index, some water status -related characteristics, and a slight decrease in fruit size and yield, PRD was considered an effective water-saving strategy with no discernible effect on fruit technological attributes.