Reviewing current knowledge on olive (Olea europaea L.) adventitious root formation

Abstract

Olive (Olea europaea) is one of the most important fruit species in the Mediterranean basin, where 95% of the world's olive orchards are planted, and it has become an economically valuable crop worldwide, due to an increasing interest in olive oil for human consumption. New olive orchards are being planted outside the Mediterranean, calling for an effort to identify the genotypes best adapted to the new conditions. However, some olive cultivars remain difficult to propagate, which significantly reduces the capacity to use the full genetic diversity of the species. Improving rooting ability in cuttings from recalcitrant olive cultivars has become a critical topic, which implies fundamental research on the anatomy, physiology, biochemistry and genetics of the adventitious root formation process. Besides, the existence of different rooting behaviors among olive cultivars also makes the species a candidate model plant for these studies. Olive propagation techniques evolved through time from field-or nursery-planted hardwood cuttings, to semi-hardwood cuttings in greenhouses under mist, and, more recently, to in vitro culture techniques. Nevertheless, research about adventitious root formation carried on each propagation method was mostly based on trial and error approaches. Researchers have mainly investigated different factors involved in the process of adventitious rooting by testing their effect in the rooting capacity of different cultivars, leading to a high dispersion and fragmentation of the available information. The goal of this review is to present the most relevant results achieved on adventitious root formation in olive cuttings, aiming to provide an integrated perspective of the current knowledge.

Rizobactérias e desenvolvimento de mudas a partir de estacas semilenhosas de oliveira (Olea europeae L.)

“…Interações microbiológicas que envolvem o crescimento e desenvolvimento são fundamentais em processos de formação das mudas de oliveira, podendo ser encontrado microrganismos como fungos micorrízicos arbusculares, que proporcionam um incremento no desenvolvimento das estacas já enraizadas, aumentando o sistema radicular, bem como a parte aérea das plantas (Ferreira et al, 2015), e também bactérias que promovem o crescimento das plantas por meio de polímeros e hormônios produzidos (Montero-Calasanz et al, 2013). No entanto, a maioria dos estudos envolvendo enraizamento ou crescimento de mudas de oliveira concentra-se em fatores químicos (Porfírio et al, 2016) e poucos são os trabalhos que consideram as interações microbiológicas, essenciais nas etapas iniciais de produção.…”

“…O método de propagação vegetativa mais utilizada na olivicultura é a estaquia devido, principalmente, a sua simplicidade e capacidade de formação de raízes adventícias pelas estacas (Porfírio et al, 2016). Diferentes cultivares de oliveira apresentam respostas distintas quanto ao enraizamento das estacas, sendo que a época do ano pode influenciar nesse processo, devido ao estado fenológico das plantas .…”

Tracking biochemical changes during adventitious root formation in olive (Olea europaea L.)

“…Among the factors that may influence adventitious rooting (reviewed in Porfirio et al, 2016a), oxidative enzymes and auxins are the most studied and discussed. The involvement of auxins in adventitious rooting has been studied for a long time (Wiesman et al, 1989) and they are extensively used in plant propagation protocols as root-inducing compounds (Preece, 2003).…”

“…The two main natural auxins are indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), quantified by various methods, as recently revised by Porfirio et al (2016b). Evidence suggests that IAA possibly promotes adventitious rooting through a signaling network similar to that happening in lateral roots, involving auxin response factors (ARF) and other plant hormones (Porfirio et al, 2016a). On the other hand, IBA auxin activity seems to be a result of its conversion into IAA (Korasick et al, 2013) by peroxissomal enzymes Zolman et al, 2007Zolman et al, , 2008.…”

High‐resolution episcopic microscopy enables three‐dimensional visualization of plant morphology and development

“…Several studies suggested that the inhibition of adventitious root formation was related to the capacity of the tissue to initiate root primordia rather than to the presence of an anatomical barrier (Amissah, Paolillo, & Bassuk, ; Davies & Hartmann, ; White & Lovell, ). Thus far, 2D histological analyses have been applied to characterize the anatomical basis of poor rooting ability (Amissah et al, ; Ballester, San‐José, Vidal, Fernández‐Lorenzo, & Vieitez, ; Harbage, Stimart, & Evert, ; Porfírio, Gomes da Silva, Cabrita, Azadi, & Peixe, ). However, the intrinsic limitation of 2D serial sections, which provide only sporadic characterization of the tissue along the cutting base, has encumbered these attempts.…”