From the juvenile to the adult vegetative phase in olive seedlings: the transition along the stem axis

Abstract

Sexual reproduction in olive is carried out for purposes such as breeding. The seedlings evolve from the juvenile to the adult stage, and until now, only the discrete developmental phases have been investigated in detail. However, the transition process has been poorly studied in fruit trees, especially in olive. In this paper, juvenile to adult transition has been explored in 30 olive seedlings coming from the Table Olive Breeding Program of the University of Sevilla, Spain. Despite of the great variability found in the olive leaf morphological parameters, mean values increased linearly from the bottom (juvenile) to the top (adult tissue) of the seedling. An upward lineal decrease in the rooting ability was also observed for the set of seedlings evaluated. No significant differences were found for the maximum net photosynthesis (PNmax) or maximum stomatal conductance (gsmax), although the lowest values were measured at <0.5 m. For all of the analysed parameters, the transitional tissue showed intermediate values. These results show for the first time in olive that the transition along the seedling stem axis follows a clear lineal tendency with a stepwise loss of juvenile characters being the shift from juvenile to adult phase in olive not an abrupt change but a gradual process. The usefulness of a fibre optic probe with a reduced sampling surface coupled to near-infrared spectroscopy (NIRS) was evaluated. NIR analysis has been confirmed to be a useful tool to discriminate the juvenile and adult leaves, but not the transition ones.