Verticillium Wilt of Olive and its Control: What Did We Learn during the Last Decade?

Abstract

Verticillium (Verticillium dahliae Kleb.) wilt is one of the most devastating diseases affecting olive (Olea europaea L. subsp. europaea var. europaea) cultivation. Its effective control strongly relies on integrated management strategies. Olive cultivation systems are experiencing important changes (e.g., high-density orchards, etc.) aiming at improving productivity. The impact of these changes on soil biology and the incidence/severity of olive pests and diseases has not yet been sufficiently evaluated. A comprehensive understanding of the biology of the pathogen and its populations, the epidemiological factors contributing to exacerbating the disease, the underlying mechanisms of tolerance/resistance, and the involvement of the olive-associated microbiota in the tree's health is needed. This knowledge will be instrumental to developing more effective control measures to confront the disease in regions where the pathogen is present, or to exclude it from V. dahliae-free areas. This review compiles the most recent advances achieved to understand the olive-V. dahliae interaction as well as measures to control the disease. Aspects such as the molecular basis of the host-pathogen interaction, the identification of new biocontrol agents, the implementation of "-omics" approaches to unravel the basis of disease tolerance, and the utilization of remote sensing technology for the early detection of pathogen attacks are highlighted.

Keywords: Olea europaea; Verticillium dahliae; biological control agents; breeding for resistance; defoliating and non-defoliating; integrated disease management; organic amendments; pathogen detection; soil microbiota; vascular disease.

Figure 1

A super high-density hedgerow olive orchard located in Córdoba province (Spain).

Figure 2

Tag-cloud showing the most relevant keywords cited in the bibliography consulted to produce this review article. The figure was built using a free online word cloud generator [20]. The importance of each tag is visually weighted according to its frequency of use. The acronyms used are defined as follows: Arbuscular Mycorrhizal Fungi (AMF), Biocontrol Agents (BCA), Confocal Laser Scanning Microscopy (CLSM), Defoliating (D), Essential Oils (oils), Ethylene (ET), Gas Chromatography–Mass Spectrometry (GCMS), Horizontal Gene Transfer (HGT), Induced Systemic Resistance (ISR), Integrated Disease Management (IDM), Jasmonic Acid (JA), Loop-Mediated Isothermal Amplification (LAMP), Non-Defoliating (ND), Organic Amendments (OA), Plants Extracts (extracts), Plant Growth Promotion (PGP), Reactive Oxygen Species (ROS), Salicylic Acid (SA), Systemic Acquired Resistance (SAR), Transcription Factor (TF), Unmanned Aerial Vehicle (UAV), Vegetative Compatibility Groups (VCG), Verticillium Wilt of Olive (VWO), Water Disinfestation (Water), World Olive Germplasm Bank (WOGB).

Figure 3

The traditional olive trees landscape in the Mediterranean Basin. Olive cultivation is part of the history, culture, landscape, and economy of this region. It is a tree crop well adapted to Mediterranean climatic conditions.

Figure 4

Symptoms observed upon the artificial inoculation of the defoliating pathotype of Verticillium dahliae in olive plants cultivar Picual. (A) Chlorotic and distorted leaf; (B) partial severe defoliation (affecting some stems) of green leaves; (C) fully defoliated dead plant; (D) olive plants may undergo the so-called natural recovery phenomenon (see, for instance, López-Escudero and Mercado-Blanco, 2011 [16]).

Figure 5

An idealized compilation of the available Verticillium wilt of olive control measures described in this review to be implemented within an integrated management strategy. (A) Use of spectral technologies coupled with drones or UAV for the early detection of the disease at a large scale (modified form an image kindly provided by Dr. J.A Jiménez Berni, IAS-CSIC, Córdoba); (B) identification based on molecular methods; (C) dogs trained for the detection of Verticillium dahliae volatile compounds; (D) heat treatments; (E) organic amendments; (F) biological control agents; (G) the use of plant extracts and essential oils; (H) water disinfection treatments; (I) new sources of tolerance/resistance.