Endophytes Vs Tree Pathogens and Pests: Can They Be Used As Biological Control Agents to Improve Tree Health?
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Central Archive at the University of Reading Endophytes vs tree pathogens and pests: can they be used as biological control agents to improve tree health? Article Published Version Creative Commons: Attribution 4.0 (CC-BY) Open access Rabiey, M., Hailey, L. E., Roy, S. R., Grenz, K., Al-Zadjali, M. A. S., Barrett, G. A. and Jackson, R. W. (2019) Endophytes vs tree pathogens and pests: can they be used as biological control agents to improve tree health? European Journal of Plant Pathology. ISSN 0929-1873 doi: https://doi.org/10.1007/s10658-019-01814-y Available at http://centaur.reading.ac.uk/85744/ It is advisable to refer to the publisher's version if you intend to cite from the work. See Guidance on citing . To link to this article DOI: http://dx.doi.org/10.1007/s10658-019-01814-y Publisher: Springer All outputs in CentAUR are protected by Intellectual Property Rights law, including copyright law. Copyright and IPR is retained by the creators or other copyright holders. Terms and conditions for use of this material are defined in the End User Agreement . www.reading.ac.uk/centaur CentAUR Central Archive at the University of Reading Reading's research outputs online Eur J Plant Pathol https://doi.org/10.1007/s10658-019-01814-y REVIEWS Endophytes vs tree pathogens and pests: can they be used as biological control agents to improve tree health? Mojgan Rabiey & Luke E. Hailey & Shyamali R. Roy & Kristina Grenz & Mahira A. S. Al-Zadjali & Glyn A. Barrett & Robert W. Jackson Accepted: 21 July 2019 # The Author(s) 2019 Abstract Like all other plants, trees are vulnerable to The impact of environment and plant genotype on attack by a multitude of pests and pathogens. Current selecting potentially beneficial and exploitable endo- control measures for many of these diseases are limited phytes for biocontrol is poorly understood. How endo- and relatively ineffective. Several methods, including phytes synergise or antagonise one another is also an the use of conventional synthetic agro-chemicals, are important factor. This review focusses on recent re- employed to reduce the impact of pests and diseases. search addressing the biocontrol of plant diseases and However, because of mounting concerns about adverse pests using endophytic fungi and bacteria, alongside the effects on the environment and a variety of economic challenges and limitations encountered and how these reasons, this limited management of tree diseases by can be overcome. We frame this review in the context of chemical methods is losing ground. The use of biolog- tree pests and diseases, since trees are arguably the most ical control, as a more environmentally friendly alterna- difficult plant species to study, work on and manage, yet tive, is becoming increasingly popular in plant protec- they represent one of the most important organisms on tion. This can include the deployment of soil inoculants Earth. and foliar sprays, but the increased knowledge of mi- crobial ecology in the phytosphere, in particular phyllo- Keywords Endophytes . Biological control . Trees . plane microbes and endophytes, has stimulated new Pathogen . Pest . Disease thinking for biocontrol approaches. Endophytes are mi- crobes that live within plant tissues. As such, they hold potential as biocontrol agents against plant diseases Introduction because they are able to colonize the same ecological niche favoured by many invading pathogens. However, Importance of trees and their diseases the development and exploitation of endophytes as bio- control agents will have to overcome numerous chal- Being some of the largest organisms on Earth, trees in lenges. The optimization and improvement of strategies forest and woodland settings cover 40% of the Earth’s employed in endophyte research can contribute towards terrestrial surface (Fao 2010). This forms a major part of discovering effective and competent biocontrol agents. the global biomass and provides habitat for large num- bers of animal and plant species with varying levels of association. To humans, the importance of trees for * : : : : M. Rabiey ( ) L. E. Hailey S. R. Roy K. Grenz food, timber and non-timber resources has been histor- M. A. S. Al-Zadjali : G. A. Barrett : R. W. Jackson School of Biological Sciences, University of Reading, Knight ically and widely identified (Cazorla and Mercado- Building, Reading RG6 6AJ, UK Blanco 2016). Carbon sequestration is one of the most e-mail: [email protected] significant ecosystem services provided by trees, with Eur J Plant Pathol total carbon stocks in UK forests (including soil) alone Sjöman and Busse Nielsen 2010). Monocultures also calculated at 800 megatons (Quine et al. 2011). pose a specific problem, as plants grown in monoculture The economic value of trees and shrubs in urban are more susceptible to pest and disease outbreaks and landscapes has been increasingly recognised since the are sensitive to changes in climate, which are less likely turn of the millennium, with the popularisation of elec- with polycultures (Sjöman et al. 2012). Lax biosecurity, tronic tools for estimating this value, e.g. i-Tree soft- including the importation of planting stock and tree ware, and research revealing a suite of functional bene- products, can also drive biological invasions by tree fits; providing habitat to urban wildlife, reducing air pests and diseases, as has been demonstrated in Europe pollution, intercepting rainfall, shading and reducing (Brasier 2008; Epanchin-Niell 2017; Potter et al. 2011). heat absorption by man-made surfaces (Binner et al. Some non-native pests are highly destructive and can 2017; Nowak 2004; Tyrväinen et al. 2005;Xiaoand cause substantial damage to forests and urban/suburban Mcpherson 2002). The cultural services provided by trees (Aukema et al. 2011). Such invasions often lead to trees are also significant, offering both physical significant changes in forest structure and species com- and mental health benefits. The capitalised value position, which in turn lead to changes in ecosystem of the social and environmental benefits provided functions (Lovett et al. 2016). Given the range of pests by woodlands and forests in the UK alone was and diseases that trees are facing, the long generation estimated to be over £29 billion (Lawrence et al. 2009; time of trees, the practical difficulty of working with Willis et al. 2003). many of them, and also the speed with which the envi- However, trees in particular can be susceptible to ronment is changing, we are faced with a very difficult attack from pests and diseases (Table 1), especially if challenge – how do we improve our disease and pest invading from other geographical locations management to help trees survive? (Hansbrough 1965; Tubby and Webber 2010). Most diseases are caused by microbial pathogens (fungi, bac- Classical control approaches for tree pests and diseases teria and viruses), the effects of which are amplified during periods of unfavourable environmental condi- The application of plant protection products (PPPs) for tions including unseasonal temperature shifts and ex- the control of tree pests and diseases is already often tremes in rainfall patterns (Cazorla and Mercado-Blanco limited by ecological concerns and modulated by the 2016) and anthropogenic climate change (Dukes et al. particular local context, as exemplified by the varied 2009; La Porta et al. 2008; Sturrock 2012; Sturrock et al. management of oak processionary moth, Thaumetopoea 2011; Tubby and Webber 2010). processionea., in Europe (Tomlinson et al. 2015). How- Tree pest invasions are also increasing alongside ever, PPPs are well accepted within commercial tree climate change and expanded global trade and may act fruit production and the tree care industry of North in tandem with native or invasive diseases, as vectors or America. co-occurring on hosts, to greatly reduce the populations Presently, PPPs are generally synthetic chemicals that of particular tree species (Brasier 2008;Tubbyand disrupt the cellular function, or life cycle of the target Webber 2010), with the potential to ultimately cause organism. Other PPPs work on a physical basis e.g. their local extinction. killing insect or acarid targets on contact via suffocation, Plant susceptibility to pests and diseases is often or abrasion of the exoskeleton and subsequent desicca- related to the stress level of the individual. Unfortunate- tion. These products are typically those formulated for ly, trees in urban areas, which have a particularly high use in agriculture. Aboveground and external tree pests value to humans, often face high stress levels. In urban and diseases are often controlled with aqueous sprays of areas, stress can arise from mismatching of the planting PPPs to the foliage and bark. Specialised high-pressure stock’s ecological traits to the planting site, root defor- spray systems can be used for such applications to large mities, damage and desiccation, planting at improper trees (Hirons and Thomas 2018). depths in unsuitable soils, poor nutrient and water avail- Internalised pests and diseases, such as nematodes, ability, and increased exposure to pollutants, xenobiotics are more difficult to reach due to their physical conceal- and contaminants (Aldhous and Mason 1994;Ferrini ment within the host; adjuvants (additives) may improve and Nicese 2002; Gilman et al. 2015; Grossnickle 2005; the penetration of externally applied PPPs for such Pauleit 2003; Percival et al. 2006;Pfeifferetal.2014; targets e.g. through bark (Garbelotto et al. 2007), Eur J Plant Pathol Table 1 Examples of some current major pathogens and pests of trees Pathogen Host Symptoms Reference Oomycete Phytophthora Larix spp. and Quercus Shoots and foliage can be affected. Visible as Davidson et al. (2003) ramorum spp. (sudden death) wilted, withered shoot tips with blackened needles.Treeswithbranchdiebackcanhave numerous resinous cankers on the branches and upper trunk. It has killed millions of native oak and tan-oak trees in the USA Fungus Ceratocystis Quercus spp.