Water status modifies the relative sink activity of mesocarp, endocarp and oil during olive fruit development

Abstract

Olive fruit growth requires not only overall importation of assimilates but the distribution of those assimilates among the different sinks within the fruit, principally pulp (mesocarp), pit (endocarp), seed, and oil. The classical view of olive fruit growth, generally providing the theoretical background for irrigation management strategies, perceives the biphasic pattern as representing changes in sink priorities within the fruit. However new advances, such as the relationship of endocarp growth and hardening and the occurrence of uni-phasic fruit growth under irrigation, require revisiting the classical view and offer new information regarding the competition among olive fruit tissues for assimilate supplies required for expansive growth, endocarp hardening and oil accumulation. Our study explores these relationships and the influence of water stress. In an ‘arbequina’ olive orchard two irrigation treatments were used: T0 irrigated following the FAO strategy and T1, under rainfed conditions until maximum endocarp hardness, then irrigated to maintain equal stem water potential to T0. Four repetitions per treatment were used, in randomized blocks. Fruit samples were collected weekly and dry weight of fruit tissues, oil content and endocarp hardness (resistance to breakage) determined. Water stress principally reduced endocarp dry matter accumulation even affecting pit-breaking pressure but not pit hardening timing. After pit hardening ended, dry weight of mesocarp-excluding-oil remained constant. Oil accumulation was a dominant sink, competing favorably against endocarp lignification from as early as mid-pit hardening and consistently showing low sensitivity to water stress.