Analysis of primary and secondary growth and modelling growth dynamics of olive shoots (Olea europaea L.)

Abstract

SummaryUnderstanding growth rate in woody plants is an essential criterion for the establishment of tree architecture, and therefore of future tree form. Olive seedlings exist as three main tree structures: bushy, mixed, and tree-form. Growth dynamics were observed on different types of shoots of these different forms throughout the growing season. Both primary growth (elongation and developed metamers) and secondary growth (basal diameter increment) were considered. To study the inter-annual pattern of shoot growth, simple linear regressions were performed between shoot properties measured at the beginning and at the end of the vegetative season. Positive correlations were obtained for all growth parameters. Allometric relationships between primary and secondary growth indicated that the increment in basal diameter was related to primary growth. Bud size and the contents of primordia were compared to the structure of the future shoot and leaves produced after the Spring and Autumn growth flushes. Shoots were entirely preformed in the bushy form. Mixed- and tree form-types had a preformed portion, followed by a neoformed portion. Mathematical models on olive growth were developed based on growth dynamic parameters. Elongation and metamer numbers showed a tri-sigmoid evolution (two Spring flushes and an Autumn flush) which was modelled by theoretical equations defined by tri-logistic functions, and characterised by nine parameters. Secondary growth was also represented by three logistic shapes, indicating three phases of girth expansion on all three forms. These results indicate that olive tree growth is rhythmic under the rain-fed conditions of Tunisia.