Irrigation differently affects endocarp and mesocarp growth during olive fruit development

To determine the growth response of the olive fruit mesocarp and endocarp to tree water status we subjected field-grown trees (Olea europaea L. 'Leccino') to different irrigation regimes. Tree water status was assessed as pre-dawn leaf waterpotential (Ψw), fruit tissue growth as fresh weight (FW) and dry weight (DW). Fruit weight responded readily to Ψw and reflected differences in tree water status. Mesocarp FW was positively correlated to Ψw and the response was evident starting at 15 weeks after full bloom (AFB) through harvest. The endocarp FW responded weakly to severe water deficit and by 15 weeks AFB had grown to full size. The pulp/pit ratio, expressed on FW basis, tended to decrease as the level of water deficit increased with Ψw below -2 MPa. The mesocarp DW was unaffected by tree water status at 9 weeks AFB and only slightly decreased when Ψw was less than -2 MPa at 20 weeks AFB. The results indicate how the behavior of different tissues and growth processes during fruit development affect the overall fruit response to water status.