Plant Pathology and Plant Pathogens. John A. Lucas

subject, and to place the phenomenon of plant disease in a wider biological context. Research in plant pathology can be broadly divided into tactical and strategic aspects. The former is concerned with providing solutions to disease problems by identifying causal agents and evaluating the most cost‐effective options for their control. The latter is longer term and aims to understand fundamental aspects of plant disease such as pathogen ecology, population biology, host–pathogen interactions, and plant immunity. This knowledge can then be applied to devise improved methods of disease control.

The book is divided into three parts. The first focuses on the problem of plant disease, the causal agents and their significance, disease diagnosis, and the development of epidemics in plant populations. This account highlights the influence of environmental factors on the multiplication and spread of pathogens, and the use of climate data in disease prediction. The second part deals with host–pathogen interactions: how pathogens gain entry to the host, how their growth and development in the plant lead to disease symptoms, and how the plant responds. The outcome of any host–pathogen confrontation depends on a dynamic interplay between factors determining microbial pathogenicity and the active mechanisms of plant immunity. This interaction ultimately determines host–pathogen specificity, whereby any pathogen is able to cause disease in only a restricted range of host plants. Plant and molecular biologists are studying host–pathogen systems as experimental models to probe the mechanisms of gene expression and regulation, and to reveal details of the evolutionary “arms race” taking place between plants and pathogens. Part III deals with the practical business of disease control, often described as crop protection. This covers the management of disease by means of chemicals, breeding for resistance, and alternative biological approaches. Finally, the combined use of cultural practices and all these other measures to provide sustainable, integrated systems for disease control is described.

      A comprehensive treatment of individual diseases and the methods used in their control is beyond the scope of a text of this length. For the sake of brevity, specific pathogens or the diseases they cause are often mentioned without further explanation. This approach may be likened to that adopted in many ecology texts, in which the reader is expected to be familiar with most of the higher plants or animals discussed therein. There is, however, an appendix listing all the pathogens and diseases mentioned in the book, together with brief details which will enable the reader to obtain further information about particular diseases. More detail concerning specific aspects of pathology may be obtained by consulting the recommended further reading.

      Further Reading

      Books

      1 Agrios, G. (2005). Plant Pathology, 5e. Amsterdam: Elsevier Academic Press.

      2 Schumann, G.L. and D'Arcy, C.J. (2009). Essential Plant Pathology, 2e. St Paul, Minnesota: American Phytopathological Society Press.

      3 Strange, R.N. (2003). Introduction to Plant Pathology. Chichester: Wiley.

      Reviews and Papers

      1 Foley, J.A., Ramankutty, N., Brauman, K.A. et al. (2011). Solutions for a cultivated planet. Nature 478: 337–342.

      2 Godfray, H.C.J., Beddington, J.R., Crute, I.R. et al. (2010). Food security: the challenge of feeding 9 billion people. Science 327: 812–818.

      3 Savary, S., Bragaglio, S., Willocquet, L. et al. (2017). Crop health and its global impacts on the components of food security. Food Security 9: 311–327. https://doi.org/10.1007/s12571‐017‐659‐1.

      Scientific Journals

      Many scientific journals contain reviews and research papers relevant to plant pathology. One especially useful source is the Annual Review of Phytopathology. Others include:

      Advances in Botanical Research

      Annals of Applied Biology

      Crop Protection

      European Journal of Plant Pathology

      Fungal Genetics and Biology

      Journal of Phytopathology

      Molecular Plant–Microbe Interactions

Molecular Plant Pathology

      Mycological Research

      New Phytologist

      Pest Management Science

      Plant Disease

      The Plant Cell

      The Plant Journal

      Physiological and Molecular Plant Pathology

      Phytopathology

      Plant Pathology

      PLOS Pathogens

      American Phytopathological Society: www.apsnet.org

      British Society of Plant Pathology: www.bspp.org.uk

      European Foundation for Plant Pathology: www.efpp.net

      Review of Plant Pathology, an abstracts database of plant pathology research: www.cabi.org/publishing‐products/online‐information‐resources/review‐of‐plant‐pathology

1 The Diseased Plant

       Since it is not known whether plants feel pain or discomfort, and since, in any case, plants do not speak or otherwise communicate to us, it is difficult to pinpoint exactly when a plant is diseased.

      (George N. Agrios, 1936–2010)

      The significance of disease in plants varies depending upon biological, agricultural, and socioeconomic factors. At one extreme, disease may be so severe that the farmer is faced with total crop failure, and the need for control measures is immediately obvious. In other cases, it may be difficult to define disease symptoms, the cause of the problem is not initially clear, and any benefits obtained from control measures are not easy to predict. This chapter discusses the nature of disease and surveys the range of pathogens, pests, and other agents which adversely affect plants. The impact of disease, both in natural plant communities and in agriculture, forestry and horticulture, is then considered.

Concepts of Disease

      To fully understand the nature of disease, one must first identify the processes occurring during the growth and development of the healthy plant. Such an analysis may be done at three levels:

       the sequence of events comprising the normal plant life cycle

       the physiological processes involved in plant growth and development

       the metabolic pathways and molecular reactions underlying these processes.

Seed germination, maturation of vegetative structures, the initiation of reproduction, and the formation and dispersal of fruits and seeds are all critical phases of the life cycle at which disease may occur (Figure 1.1). At each stage in this developmental sequence, the integration of several physiological processes is essential for the continued development of the plant. Cell division and differentiation, the fixation and utilization of energy (photosynthesis and biosynthesis), transport of water and nutrients (transpiration and translocation), and storage of reserve compounds are all necessities for growth. Each of these functions involves a complex series of molecular events which comprise the overall metabolism