Effect of deficit irrigation during the oil synthesis period on carbohydrate content in olive 'Arbequina' hedgerows

During the oil synthesis and accumulation period, olive fruits are the main carbohydrate sink. Water stress may modify oil synthesis and reserve availability for the next season's development. The objective of this study was to evaluate the effect of deficit irrigation during fruit oil synthesis on next season's carbohydrate content. The experiment was carried out in a super-high-density olive 'Arbequina' orchard located in La Puebla de Montalban, Toledo, Spain (39 degrees 48'N 4 degrees 27'W; 516 m a.s.l.). Two irrigation levels were applied from the middle of August until harvest (1 November), when most of the 80% oil accumulation in fruits occurs. The control treatment (non-stressed) was irrigated until harvest, trying to maintain the root zone close to field capacity. The stressed treatment was irrigated with 12% of non-stress treatment. Carbohydrates (soluble sugars and starch) were measured in roots, leaves and stems at the end of winter. Differences in carbohydrate concentration were observed in leaves but not in reserve organs such as roots or stems. Leaves of the stressed trees presented higher carbohydrate contents. These results show the important role of carbohydrates in water stress adaptation by osmotic regulation.