فایل ورد کامل مقاومت القا شده به آفات و پاتوژن ها در درختان

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تعداد صفحات این فایل: ۲۷ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Induced resistance to pests and pathogens in trees~~en~~

Abstract

Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco-friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR-based management tools in forest systems.

۱ Introduction

In any plant–insect and plant–pathogen interaction there is a continuum of possible outcomes, ranging from extreme susceptibility to complete resistance. Plant resistance can be described on several mechanistic levels. These include basal resistance, parasite- and race-specific resistance (Jones & Dangl, 2006; Kiraly et al., 2007), age-related (ontogenetic) resistance (Develey-Rivie`re & Galiana, 2007), organ-specific resistance (Blodgett et al., 2007) and acquired or induced resistance (IR) (Agrawal et al., 1999). In its broadest sense, IR is a form of resistance caused by activation of the host plant’s own genetically programmed defence pathways, resulting in changes that diminish the effects of subsequent biotic attack (Agrawal et al., 1999; Hammerschmidt, 2007). IR elicited by microorganisms in plants to other pathogenic microorganisms has been recognized for over 100 yr (Chester, 1933). By contrast, knowledge of plant resistance induced by insect herbivores has had a much shorter history of < 40 yr (Green & Ryan, 1972).

Most of the current knowledge on plant defence mechanisms, particularly as they relate to IR, has been obtained through studies on herbaceous annuals or short-lived perennials. These include the model plant species, Arabidopsis thaliana, Cucumis sativus (cucumber), Lycopersicon spp. (tomato), Medicago truncatula, Nicotiana tabacum (tobacco), Oryza spp. (rice), Solanum spp. (potato) and Zea spp. (maize). Many comprehensive overviews have been published on IR in herbaceous plants (Karban & Baldwin, 1997; Agrawal et al., 1999; Gatehouse, 2002), but much less is known for trees, both angiosperms and gymnosperms. Tree and herbaceous species share common plant features but trees have certain unique features when compared with herbaceous plants. They are usually much larger, have much longer life spans (sometimes of millennia), characterized by life histories that have no equals among herbaceous model plants, and exhibit different architectural forms linked to secondary growth. Trees may be subject to different patterns of herbivore and pathogen pressure and require different modes of protection. In view of this, while we draw from the knowledge gained in the more studied herbaceous model species, findings from these models may not always apply to forest trees (Hammerschmidt, 2006).

Induced resistance has been well studied in many horticultural and agricultural systems and its application has proved effective (Vallad & Goodman, 2004; Walters, 2009). For example, the synthetic chemical primer activator, acibenzolar-S-methyl (trade name Actigard or Bion, Syngenta Crop Protection, Basel, Switzerland), has been successfully used as a broad-spectrum crop protectant in the past decade (Leadbeater & Staub, 2007). IR does not involve the manipulation of genes, therefore the societal issues that are associated with the use of genetically modified organisms are not relevant to IR tools. IR functions as a multilayered, highly integrated defence system, and therefore IR can be durable and effective against a wide spectrum of pests and pathogens (Vallad & Goodman, 2004). These features are of particular importance in trees that are long-lived and confined to a particular pest environment, often for decades and even centuries.

Current methods of pest and disease management in trees vary greatly (Eyles et al., 2008). They can range from the deployment of resistant material and pesticide application, through to the use of biological control and silvicultural management. In many cases, because of economic and environmental constraints, very little is done. While the development of tree protection methods based on IR mechanisms is still very much in its infancy, IR could provide alternative forms of protection in the future, either applied with other management tools or used alone. The use of IR has the potential to offer more eco-friendly options than current pesticides available for forest trees. In this review, we summarize findings from recent ecological and molecular studies on IR to both pests and pathogens in trees. In Section II, we describe the inducible defence mechanisms underlying IR, followed by a discussion on the systemic aspects of IR (Section III) and the phytohormone signalling networks that regulate IR (Section IV). In Section V, we highlight the large knowledge gaps that will need to be addressed in order to realize the potential offered by the application of IR in forest systems.

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