A detailed description of morphological and anatomical characters of olive (Olea europaea) fruits in relation to phenological growth stages

This paper describes both morphological and anatomical changes of olive (Olea europaea) fruits of Nevadillo variety, growing under rainfed conditions, in relation to the phenological stages of fruit formation and development described by the Biologische, Bundesantalt, Bundessortenamt and Chemische Industrie (BBCH) scale. Mesocarp transverse area (TA(m)), total number of cells and TA per cell were measured in mesocarp equatorial transverse sections of the fruits. Changes in cell dimensions and shape along the mesocarp radial longitudinal section and endocarp sclerification were also analysed. The pattern of fruit growth showed linear increases in TA(m), coupled with the whole fruit TA (TA(f)) increases throughout its whole developmental period. This observation disagrees with the classical growth model which suggested that the growth of a drupe adjusts to a double sigmoid curve. A strong correlation between TA(m) and TA(f) and a weak correlation between endocarp TA and TA(f) were observed. The tissue organisation in the cross-sectional area of the fruit agrees with previous histological descriptions. Cell organisation in the longitudinal radial plane of the olive fruit was established for the first time: a single-layered epidermis; a hypodermis: first four layers of subepidermal parenchyma cells; an outer mesocarp: from the layer 5 to layer 24 to 27 and an internal mesocarp: following layers of parenchyma cells up to the vascular bundles. Until now, comparative anatomical studies on olive fruit have been carried out only in the cross section, that is, in two dimensions. The anatomy of longitudinal section described here, together with the cell organisation in the transverse plane, will allow designing a tridimensional model of the fruit anatomy. This model will be useful to interpret the cell processes (division and expansion) involved in fruit growth, morphogenesis and oil storage, and to explore how climate and agricultural management practices could impact on olive fruit development on Nevadillo and other cultivars under different growing conditions (e.g., water status and temperature variations).