Plant Pathogen Resistance Biotechnology

David B. Collinge

• Publisher: Wiley-Blackwell
• Year: 2016
• Print ISBN: 9781118867761
• eBook ISBN: 9781118867730
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biotechnology
• Index: Biological Sciences

Plant pathogens and diseases are among the most significant challenges to survival that plants face. Disease outbreaks caused by microbial or viral pathogens can decimate crop yields and have severe effects on global food supply. Understanding the molecular mechanisms underlying plant immune response and applying this understanding to develop biotechnological tools to enhance plant defense against pathogens has great potential for moderating the impact of plant disease outbreaks. Plant Pathogen Resistance Biotechnology's main focus is an in depth survey of the biological strategies being used to create transgenic disease resistant plants for sustainable plant resistance

Plant Pathogen Resistance Biotechnology is divided into four sections. The first section covers biological mechanisms underpinning disease resistance in plants, while the second highlights case studies of important pathogen-crop groups and then considers why the application of important pathogen-crop groups, transgenic-based strategies designed to selectively target pathogens could benefit crop production. The third section provides information on the status of transgenic crops around the world, and finally the last part explores high-tech alternatives to genetic engineering for developing disease resistant traits in plants.

Edited and authored by leaders in the field, Plant Pathogen Resistance Biotechnology will be an invaluable resource to those studying or researching plant biotechnology, plant pathology, plant biology, plant and crop genetics, in addition to crop science.

Chapter 1
The Status and Prospects for Biotechnological Approaches for Attaining Sustainable Disease Resistance

David B. Collinge¹, Ewen Mullins², Birgit Jensen¹ and Hans J.L. Jørgensen³

¹ Section for Microbial Ecology and Biotechnology, Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre, University of Copenhagen, Copenhagen, Denmark

² Department of Crop Science, Teagasc Crops, Environment and Land Use Programme, Carlow, Ireland

³ Section for Plant and Soil Science, Department of Plant and Environmental Sciences and Copenhagen Plant Science Centre, University of Copenhagen, Copenhagen, Denmark

1.1 Introduction

Plant pathogens constitute major constraints on crop yield. In fact, a recent conservative estimate suggests that crop diseases are responsible for average annual yield losses of 10% (Chakraborty and Newton, 2011). For example, late blight of potatoes, caused by Phytophthora infestans, is estimated to cause annual losses of over €5 billion worldwide (Chapter 9). Another disease complex, Fusarium head blight, represents a more complex problem because the disease not only affects yield, but also contaminates food and fodder with mycotoxins which impact negatively on the health of both humans and livestock (Buerstmayr and Lemmens, 2015).

Several factors suggest that the negative impact of advancing plant diseases is increasing. For example, increasing areas of monoculture with reduced rotation to meet food productivity and profitability increases crop vulnerability to pathogenic microorganisms. This is matched by the erosion of crop management systems as witnessed by, for instance, the alarming increase in fungicide resistance within cereal pathogens (Cools and Fraaije, 2012). Furthermore, the passive spread of opportunistic pathogens has increased as a consequence of globalisation, which has promoted open markets across continents. A recent example in Europe is the East Asian fungus Hymenoscyphus fraxineus, a saprophyte of Fraxinus mandshurica. This was not known as a pathogen before colonisation and subsequent decimation of European ash (Fraxinus excelsior) populations was observed in Eastern Europe about 20 years ago (reviewed by McKinney et al., 2014). Climate changes are also assisting the spread of crop pathogens, as evidenced by the devastating migration of coffee rust (caused by Hemileia vastatrix) strains across the central and northern parts of South America into coffee plantations at higher altitudes, which were previously not attacked (Ghini et al., 2011).

But how can the alarming progression of crop diseases be halted? There are several methods which can contribute to the control of plant diseases. Good farm management is always a prerequisite, but other measures, especially disease resistance obtained by classical breeding and the use of pesticides, are highly important to secure food production worldwide. Furthermore, biological control and induced resistance are promising alternatives, especially in sustainable and integrated pest management strategies (Strange and Scott, 2005; Chapters 17 and 18). Yet, when taken individually, each of these methods has its limitations, and none can stand alone to solve all the problems in the effort to feed the increasing world population.

We believe that the employment of biotechnology-based approaches can contribute towards developing more effective and higher levels of disease control. The development of transgenic disease resistant plants is only one – albeit the most obvious – way of exploiting these biotechnological approaches (Campbell et al., 2002; Chen et al., 2012; Collinge et al., 2008; Collinge et al., 2010; Fuchs and Gonsalves, 2007; Gurr and Rushton, 2005a; Gurr and Rushton 2005b). Indirect biotechnological approaches, such as marker-assisted breeding, as well as the exploitation of association genetics and genomic selection, are closely-linked methods where the identification of genes responsible for specific traits can be used to develop gene-specific molecular makers to accelerate the process of conventional breeding and/or make it more efficient (Mammadov et al., 2007; Moose and Mumm 2008; Chapter 19, this volume). In addition, the development and understanding of alternative control measures, including induced disease resistance (Chapter 17) and biological control (Chapter 18), has benefited from the application of multiple biotechnological approaches coupled with molecular and cellular approaches.

Among the thousands of species of plant pathogenic microorganisms, only a small minority have the capacity to infect a broad range of plant species. Most pathogens instead exhibit a high degree of host specificity and only cause disease in one or a few hosts. On the other hand, most hosts are susceptible to a number of pathogenic species. Therefore, different host-pathogen interactions represent different challenges, agronomically, biologically and ecologically. This chapter provides an overview of the mechanisms of disease resistance, which show the greatest potential for being targeted by GM approaches, and discusses how our increased understanding of the processes of plant defence can lead to improved disease control. In addition, the technical and biological constraints which are likely to hamper the successful development of GM crops are exemplified and discussed.

1.2 Factors to consider when generating disease-resistant crops

Disease resistance or, at the cellular level, plant immunity, is complex and depends on a plethora of independent but interacting physiological mechanisms. This section introduces important pathogen and host factors involved in the interaction between pathogens and their hosts. This is the platform for successful manipulation of the plant to achieve resistance.

1.2.1 The diversity and life styles of microbial pathogens

Many types of organisms can cause diseases in plants. Prokaryotes and eukaryotes themselves are highly diverse, and the latter encompasses three important kingdoms: Fungi, Chromista (oomycetes) and Protozoa (plasmodiophrids). In addition, viruses constitute a highly specialized type of pathogen. Collectively, this means that pathogens differ physiologically, and therefore different individual physiological mechanisms in the host plant (e.g., individual antimicrobial factors, such as chitinases or phytoalexins), will often contribute to arrest growth of specific pathogens.

Pathogenic microorganisms interacting with plants exhibit several lifestyles which are best characterized in terms of the trophic interactions at the different phases in their respective life cycles. The pathogenic lifestyles can be manifested as biotrophy (Fig. 1.1a), necrotrophy (Fig. 1.1b) or hemibiotrophy (Fig 1.1c), where the amount of direct visible damage to the host increases accordingly, dependent on the duration of infection. The biotrophic lifestyle is exhibited by pathogens that are dependent on acquiring nutrition from a living cell, so if a host cell dies, the pathogen also dies. Important examples are oomycetes causing downy mildews (e.g., Peronspora spp.), the ascomycetes causing powdery mildews (e.g., Blumeria spp.) and the basidiomycetes causing rust (e.g., Puccinia spp.). These biotrophic pathogens rely on specialized feeding structures termed haustoria to obtain nutrients from the host. In contrast, a pathogen with a necrotrophic lifestyle obtains its nutrition from dead cells. Necrotrophs typically use toxins and hydrolytic enzymes to kill the host and are often characterized by a broad host range. There appear to be relatively few true necrotrophic pathogens. Important examples are Botrytis cinerea and Sclerotinia sclerotiorum, although many organisms have been classified as such. Between the biotrophic and necrotrophic pathogens is a third group of pathogens classified as hemibiotrophic due to an apparent biotrophic, or perhaps endophytic, stage after initial infection, which is then followed by a visible necrotrophic phase leading to host death. Examples include Phytophthora infestans in potato and Zymoseptoria tritici in wheat, and many important bacteria especially Pseudomonas syringae and Xanthomonas spp pathovars. Hemibiotrophic pathogens are quite heterogeneous, ranging from organisms with a predominantly biotrophic lifestyle (Z. tritici) to organisms exhibiting predominantly necrotrophic features such as toxin production. Examples of the latter include victorin produced by Bipolaris victoriae which can introduce programmed cell death in its host, oat, and ToxA produced by Drechslera tritici-repentis in wheat (Curtis and Wolpert, 2002; Howlett, 2006; Pandelova et al., 2009).

Fig. 1.1 Selected plant pathogen interactions illustrating lifestyle and the effects of specific types of pathogenicity factor. (a) The biotrophic pathogen Blumeria graminis f.sp. tritici (ascomycete) on wheat (Triticum aestivum). Note that the plant tissue is largely green and that there is profuse conidial sporulation as well as chasmothecia (cleistothecia). (b) The necrotrophic pathogen Botrytis cinerea on raspberry (Rubus idaeus). Note tissue collapse. (c) The hemibiotrophic fungal pathogen Phoma lingam on oilseed rape (Brassica napus). Note chlorosis in ...

Table of contents

• Cover
• Title Page
• Table of Contents
• List of Contributors
• Foreword
• Acknowledgments
• Chapter 1: The Status and Prospects for Biotechnological Approaches for Attaining Sustainable Disease Resistance
• Part I: Biological Strategies Leading Towards Disease Resistance
• Part II: Case Studies for Groups of Pathogens and Important Crops. Why Is It Especially Advantageous to use Transgenic Strategies for these Pathogens or Crops?
• Part III: Status of Transgenic Crops Around the World
• Part IV: Implications of Transgenic Technologies for Improved Disease Control
• Index
• End User License Agreement