Effect of varied summer deficit irrigation on components of olive fruit growth and development

• Summer water reduction timing and intensity differentially affect olive fruit growth.
• Mesocarp cell growth decreased directly in relation to irrigation but showed recovery.
• Fruit water composition responded most to irrigation level but oil was unaffected.
• Endocarp growth was affected when irrigation reduction was early.
• Late irrigation reductions produced epidermal cell size decrease at harvest.

The timing, duration, and intensity of summer water restrictions differentially affect overall olive fruit growth and production, based on the underlying fruit developmental processes. For that, the fruit component and tissue morphogenetic response to different irrigation strategies during summer was examined in a hedgerow olive orchard cv. Arbequina. Control trees (CON) were irrigated to maintain the root zone close to field capacity throughout fruit growth. From budburst to 4 weeks after full bloom (WAFB) (Period 1) and from 14 WAFB to harvest (at 23 WAFB) (Period 4) trees of all treatments were irrigated as CON. Two severe water deficit treatments were applied during summer by irrigating 30% CON from 4 to 9 WAFB (Period 2) in DI-P2 or from 9 to 14 WAFB (Period 3) in DI-P3. Moderate water deficit was applied in Periods 2 and 3 by irrigating 50% CON in DI-P2&3. Growth and development of the fruit and its component tissues (exocarp, mesocarp and endocarp), fruit composition, mesocarp cell area and cell number, and epidermal characteristics at the end of each period were evaluated. Water deficits significantly reduced fruit volume at the time when they were applied. Mesocarp size was more sensitive to water deficit than endocarp size and showed a high recovery capacity after rewatering. Although the majority of cells were developed in Period 1, a substantial number of mesocarp cells were also formed later. While mesocarp cell number was unaffected by water reduction in any of the deficit periods, cell size was highly affected but with high recoverability. Endocarp size was reduced when water restriction was applied in DI-P2 and its effect continued until harvest. Fruit oil content at harvest was not significantly affected by the applied water restrictions, whereas water was the fruit component which most responded to both the increases and decreases in irrigation. Cuticle thickness, epidermal cell size and number at harvest appeared to respond to both irrigation regime and fruit expansion pressures.

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