Physiological Plant Pathology

Plant pathology embraces all aspects of biological and scientific activity which are concerned with understanding the complex phenomena of diseases in plants. Physiological plant pathology represents those specialities within plant pathology which focus on the physiological and biochemical activities of pathogens and on the response of host plant tissues. Today there is an increasing recognition on the part of the scientific agri­ cultural community that only through a deeper and more fundamental under­ standing of all the interacting components of the agricultural biota can we expect to improve our capabilities of feeding an expanding world population. It is in this context that physiological plant pathology has assumed new significance within the broader field of plant pathology. No longer are studies on the biochemistry and physiology of pathogens and pathogenesis merely isolated academic exercises; rather, a substantial coherent body of knowledge is accumulating upon which our understanding of the process of disease developmen t and host resistance is being founded. It is from these foundations of knowledge that ultimately new insights into the control of plant diseases may be expected to grow. It seems appropriate, therefore, that at regular intervals those involved in the various subspecialities encompassing the broadest aspects of physiological plant pathology reassess the contributions within the particular specialities in the light of new knowledge and technologies for the purpose of articulating new and productive directions for the future.

1. General.- 1.1 History of Physiological Plant Pathology.- 1.2 Some Aspects of Host-Pathogen Interactions.- 1. Introduction.- 2. The Response of the Host.- 2.1 Resistance.- 2.2 Susceptibility.- 2.3 Economic Damage and Tolerance to Disease.- 2.4 Symptom Expression and Spurious Effects.- 3. Pathogenicity and Virulence.- 4. The Influence of Disease in the Design of Experimental Procedures.- 5. The Control of Host-Pathogen Interactions.- 5.1 Genetic Control.- 5.2 Flor’s Gene-for-gene Hypothesis.- 5.3 Metabolic Control.- 5.4 Modes of Inheritance and Induced Resistance versus Induced Susceptibility.- 5.5 Recognition Phenomena in Specificity.- 5.6 The Influence of Environment.- 6. Special Topics.- 6.1 Quantitative Measures of Disease and of Pathogens.- 6.2 Genetic Control of Experimental Material.- 6.3 Model Systems.- 6.4 Challenge Inoculations.- References.- 2. Spore Germination and Its Regulation.- 2.1 Control of Spore Germination and Infection Structure Formation in the Fungi.- 1. Introduction.- 2. Self-Inhibition and Stimulation of Germination.- 2.1 Germination Inhibitors from the Parent Colony.- 2.2 Germination Inhibitors in Spores.- 2.3 Self-Stimulation of Germination.- 3. Inhibitors and Stimulants of Germination in Soil.- 3.1 Soil Fungistasis.- 3.2 Stimulants in Soil.- 4. Stimulants and Inhibitors of Germination at Plant Surfaces.- 4.1 Inhibitors.- 4.2 Stimulants.- 5. Formation of Infection Structures.- 5.1 Genetic Basis of Infection Structure Formation.- 5.2 Experimental Studies on Infection Structure Formation.- 6. Conclusions.- References.- 2.2 Protein and Nucleic Acid Metabolism during Germination.- 1. Introduction.- 2. Facultative Parasites.- 2.1 Germination of Conidia.- 2.2 Germination of Zoospores.- 2.3 Germination of Basidiospores.- 3. Obligate Parasites.- 3.1 Introduction.- 3.2 Changes in Proteins and Nucleic Acids during Germination.- 3.3 Changes in Ribosome Activity during Spore Germination.- 3.4 Differentiation.- 3.5 Conclusions.- References.- 2.3 The Effect of Roots on the Activity of Soil-borne Plant Pathogens.- 1. Introduction.- 2. The Pathogen in the Soil.- 3. The Root-Soil Interface.- 3.1 The Rhizosphere.- 3.2 The Rhizoplane.- 4. The Mechanism of the Root Effect.- 4.1 Root Tissue Debris.- 4.2 Root Exudates.- 4.3 Oxygen and Carbon Dioxide.- 4.4 Volatile Emanations from Roots.- 4.5 Root Surface Effects.- 5. Methods of Studying Response of Pathogens to Roots.- 6. Behavior of Specific Pathogens.- 7. Discussion.- References.- 3. Cytology and Physiology of Penetration and Establishment.- 3.1 Cytology of Virus Infection and Virus Transport.- 1. Introduction.- 2. Methods of Study.- 3. Infection.- 4. Cytology of Virus Multiplication.- 5. Virus Aggregation, Anomalous Inclusions and Structural Changes in Infected Cells.- 6. Transport.- 7. Conclusions.- References.- 3.2 Plant Mycoplasma Diseases.- 1. Introduction.- 2. Historical Background.- 3. Terminology and Definitions.- 4. Methodology.- 5. Effects of MLO on Plants.- 6. Effects of MLO on Insect Vectors.- 7. Chemotherapy and Heat Therapy.- 8. Unsolved Problems.- 9. Summary and Conclusions.- References.- 3.3 Physiological and Cytological Aspects of the Bacterial Infection Process.- 1. Introduction.- 2. Pre-penetration.- 2.1 Motility, Aerotaxis and Chemotaxis.- 2.2 Predisposing Environmental Features.- 2.3 Morphological Barriers to Infection.- 3. Penetration.- 3.1 Natural Openings.- 3.2 Wounds.- 4. Growth of the Bacteria in vivo.- 4.1 Inoculum Size Required to Establish an Infection.- 4.2 The Sites of Bacterial Multiplication.- 4.3 Bacterial Proliferation in Connection with the Hypersensitive Reaction.- 4.4 Growth of Saprophytic Bacteria in Plant Tissue.- 5. Microbiological Antagonism and Commensalism.- 6. Summing-up.- References.- 3.4 Cytology of Penetration and Infection—Fungi.- 1. Introduction.- 2. The Use of Modern Methodology.- 3. Primary Penetration.- 3.1 Primary Penetration Types.- 3.2 The Mechanism(s) of Primary Penetration.- 4. Infection.- 4.1 Specialized Structures Associated with Infection.- 4.2 Effects of Infection on Susceptible Host Cytology.- 5. Relating Structure to Function.- References.- 3.5 Nematode Parasites of Plants, Their Ecology and the Process of Infection.- 1. Introduction.- 2. Physiology of Nematodes outside Their Hosts.- 3. Attraction and Penetration.- 3.1 Attraction.- 3.2 Feeding Behavior.- 3.3 Wall-degrading Enzymes.- 4. Nutrition.- 4.1 Cultures.- 4.2 Sex Determination.- 4.3 Growth Rates.- 4.4 Mineral Nutrition of Host.- 5. Cyto- and Histopathology.- 6. Biochemical Changes in Infected Tissues.- 7. Remarks on Breeding for Resistance.- References.- 4. Forces by Which the Pathogen Attacks the Host Plant.- 4.1 Host-specific Toxins in Relation to Pathogenesis and Disease Resistance.- 1. Introduction.- 2. The Agronomic Background.- 3. Development and Use of Toxin Bioassays.- 4. Genetic Studies of the Toxin Problem.- 5. Isolation and Characterization of Toxins.- 6. Comparative Effects of the Fungi and Their Toxins on Susceptible Cells and Tissues.- 7. The Resistant Cell in Relation to Toxin.- 8. Summary.- References.- 4.2 Non-specific Toxins.- 1. Introduction.- 2. Definitions.- 3. Production of Phytotoxic Compounds in vitro by Plant Pathogens.- 4. Assay Systems for Phytotoxicity.- 5. Purification of Toxins.- 6. Lowest Effective Concentration or Doses.- 7. Chemistry of Phytotoxic Compounds.- 8. Mode of Action of Phytotoxic Compounds.- 9. Toxins in Relation to Pathogenesis.- 10. Biosynthesis and Degradation of Toxins.- 11. Uses of Phytotoxic Compounds.- 12. Phytopathogens Which Produce Phytotoxic Compounds.- 13. Concluding Remarks.- References.- 4.3 Degradation of Plant Cell Walls and Membranes by Microbial Enzymes.- 1. Introduction.- 2. Structural Components.- 3. Enzymes Which Degrade Plant Structural Elements.- 3.1 Cell Wall Degradation.- 3.2 Membrane Degradation.- 4. Relationships of Enzymatic Alterations of Structural Constituents to Pathogenesis.- 4.1 Alterations of Cell Wall Constituents.- 4.2 Enzymatic Degradation of Membranes.- 5. Summary and Additional Considerations.- References.- 4.4 Morphogenic Determinants as Exemplified by the Crown-gall Disease.- 1. Introduction.- 1.1 Historical Background and Related Diseases.- 1.2 Gall Morphology and Structure.- 1.3 General Concepts.- 2. The Causal Agent.- 2.1 Taxonomic Relationships of the Agrobacteria.- 2.2 Agrobacterium Genetics.- 3. The Tumor Inception Process.- 3.1 Host Susceptibility.- 3.2 Wound Requirement.- 3.3 Site Attachment Requirement.- 3.4 Bacterial Metabolism Requirement.- 3.5 Complementation in Tumor Induction.- 3.6 Time of Initiation.- 3.7 Number of Cells Converted per Bacterium.- 3.8 The Tumor-Inducing Principle, Nucleic Acid and Phage.- 3.9 Role of Plant-growth Regulators.- 4. Tumor Development.- 5. Tumor Metabolism and the Autonomous State.- 6. Crown-gall and Cancer.- 7. Current Status and New Directions.- References.- 4.5 Sub-cellular Organization in Host-Parasite Interactions.- 1. Introduction.- 2. Methods for Studying Sub-cellular Organization in Plants.- 2.1 Histochemical and Immunohistochemical Methods.- 2.2 Cytochemical and Biochemical Methods.- 3. Alterations of Sub-cellular Organization during Disease.- 3.1 Organization of Cell Compartments.- 3.2 Examination of Changes in Host Lysosomes in Disease.- 4. Role of Extracellular Products in Disease.- 4.1 Extracellular Fungal Enzymes and the Death of Host Cells.- 5. Concluding Remarks.- References.- 5. Physiology of Host Response to Infection.- 5.1 Permeability Alterations in Diseased Plants.- 1. Introduction.- 2. Cell Permeability Theories.- 3. Pathological Changes in Permeability.- 3.1 Historical.- 3.2 Methods of Detection and Measurement of Permeability Changes in Diseased Plants.- 4. Relation of Permeability Alterations to Pathological Changes in Metabolism.- 4.1 Compatible and Incompatible Combinations.- 4.2 Transition Zones.- 4.3 Altered Permeability as an Initial Effect in Pathogenesis.- 5. Relation of Permeability Alterations to Pathological Changes in Ultrastructure.- References.- 5.2 Water Status and Imbalance.- 1. Introduction.- 2. Water Status of Plant Tissues.- 2.1 Components of Tissue Water Potential.- 2.2 Methods for Measurement of Pathogen-induced Changes in Tissue Water Potential and Its Components.- 3. Water Movement in Plants.- 3.1 Liquid Water Movement in the Plant.- 3.2 Pathogen-induced Resistances to Water Movement in Plants.- 4. Transpiration.- 4.1 Parameters Governing Transpiration Rate.- 4.2 Pathogen-induced Changes in Transpiration.- 5. Concluding Remarks.- References.- 5.3 The Carbon Balance of Diseased Plants: Changes in Respiration, Photosynthesis and Translocation.- 1. Introduction.- 2. Respiration.- 2.1 Historical.- 2.2 Uncoupling Factors in Disease.- 2.3 Changes in Respiratory Pathways during Infections.- 2.4 Terminal Oxidases and Electron Transport.- 2.5 The Significance of Respiratory Changes.- 3. Photosynthesis.- 3.1 Diseases Caused by Biotrophs.- 3.2 Virus Diseases.- 3.3 Diseases Caused by Facultative Parasites.- 4. Carbon Accumulation and Translocation.- 4.1 Mechanisms.- 4.2 Significance of Altered Transport.- References.- 5.4 Nucleic Acids in Host-Parasite Interactions.- 1. Introduction.- 2. Methodological Problems.- 3. Cytology of the Host Response as Related to Nucleic Acids.- 4. Quantitative and Qualitative Changes in Nucleic Acids in Infected Plants.- 4.1 Total RNA.- 4.2 Total DNA.- 4.3 Ribosomal RNA in Cytoplasm and Chloroplasts.- 4.4 Soluble RNA.- 4.5 Messenger RNA.- 5. Nucleic Acid Degrading Enzymes.- 6. Nucleotides and Nucleosides.- 7. Effects of Antimetabolites and Inhibitors of RNA and DNA Synthesis.- 8. Conclusions.- References.- 5.5 Protein Metabolism.- 1. Introduction.- 2. Recognition of the “Non-self” by the Host Plant.- 3. Changes in Protein Metabolism and Injury.- 4. Plant Responses to Mechanical Cutting.- 4.1 Wound Respiration.- 4.2 Enzyme Synthesis.- 4.3 Cell Organelle Formation.- 4.4 Enzyme Degradation or Inactivation.- 4.5 The Inducing Factor.- 5. Responses of Adjacent Noninfected Tissue to Infection.- 6. Protein Metabolism in Resistant or Susceptible Tissue Reactions.- 7. Changes in Protein Metabolism in Infected Tissue Containing Pathogens.- References.- 5.6 Natural Growth Regulators.- 5.6.1 Endogenous Cytokinins in Healthy and Diseased Plants.- 1. Introduction.- 2. Natural Occurrence of Cytokinins.- 3. Biological Properties of Cytokinins.- 4. Isolation, Identification and Quantitative Determination.- 4.1 Methods of Extraction and Purification.- 4.2 Bioassays.- 5. Origin, Metabolism and Transport of Cytokinins in the Plant.- 6. The Role of Cytokinins in Plant Diseases.- 6.1 Green-Island Formation.- 6.2 Fasciation Disease and False Broomrape Disorder.- 6.3 Crown Gall.- 6.4 Clubroot.- 6.5 Rust Gall Formation.- 6.6 Root Knot Galls.- 6.7 Other Disease Symptoms.- 6.8 Final Remarks.- References.- 5.6.2 Endogenous Auxins in Healthy and Diseased Plants.- 1. Introduction.- 2. Biological Properties of Auxin.- 3. Methods of Extraction and Chemical Analysis.- 4. Bioassay Methods.- 5. Changed Levels of Auxins in Plant Diseases.- 5.1 Fungus Diseases.- 5.2 Bacterial Diseases.- 5.3 Virus Diseases.- 6. The Origins of Changed Auxin Levels in Pathogenesis.- References.- 5.6.3 The Involvement of Ethylene in Plant Pathogenesis.- 1. Introduction.- 2. Natural Occurrence and Properties of C2H4.- 3. Methodology Used in the Identification of the Gas.- 3.1 Bioassays.- 3.2 Physico-chemical Methods.- 4. Ethylene Biosynthesis.- 5. The Production of Ethylene by Diseased Tissue.- 5.1 Ethylene and Enhanced Enzyme Activity.- 5.2 Ethylene and Disease Resistance.- 5.3 Ethylene as a Phytotoxin.- References.- 5.6.4 Endogenous Gibberellins in Healthy and Diseased Plants.- 1. Introduction.- 2. Chemical and Biological Properties of Gibberellins.- 3. Methods of Extraction and Chemical Identification.- 4. Gibberellin Bioassays.- 5. The Production of Gibberellins by Plant Pathogens and Other Micro-organisms.- 5.1 Fungi.- 5.2 Bacteria.- 6. The Involvement of Gibberellins in Plant Disease.- References.- 5.6.5 Endogenous Inhibitors in Healthy and Diseased Plants.- 1. Introduction.- 2. Natural Occurrence of ABA.- 3. Methods of Extraction and Chemical Analysis.- 4. Bioassay Methods.- 5. The Involvement of ABA in Plant Diseases.- 5.1 Stunting Syndromes.- 5.2 The Role of ABA in Wilting Plants.- References.- 5.7 Oxidative Enzymes.- 1. Introduction.- 2. Peroxidase and Catalase.- 2.1 Characteristics.- 2.2 Physiological Function.- 2.3 Function in the Infected Plant.- 3. Phenoloxidases.- 3.1 Characteristics.- 3.2 Physiological Function.- 3.3 Function in the Infected Plant.- 4. Cytochrome Oxidase.- 5. Ascorbic Acid Oxidase.- 6. Glycolic Acid Oxidase.- 7. Dehydrogenases.- 8. Conclusions.- References.- 5. 8 Phytoalexins.- 1. Introduction.- 2. Leguminosae.- 3. Solanaceae.- 4. Malvaceae.- 5. Convolvulaceae.- 6. Umbelliferae.- 7. Gramineae.- 8. Rosaceae.- 9. Compositae.- 10. Conclusions.- References.- 5.9 Preformed Substances as Potential Protectants.- 1. Introduction.- 2. Unsaturated Lactones.- 2.1 Occurrence and Distribution.- 2.2 Chemistry.- 2.3 Antimicrobial Activity.- 2.4 Role of Tuliposides.- 3. Cyanogenic Glycosides.- 4. Sulphur Compounds.- 4.1 Leek Oils.- 4.2 Mustard Oils.- 5. Phenols and Phenolic Glycosides.- 6. Saponins.- 6.1 Occurrence and Distribution.- 6.2 Saponin Determination.- 6.3 Chemistry and Biological Activity.- 6.4 Mode of Action.- 6.5 Role in Antifungal Resistance.- 7. Mycorrhiza.- 8. Inhibitors of Fungal Enzymes.- 9. Miscellaneous.- 10. Role of Preformed Inhibitory Substances.- References.- 5.10. Metabolic Regulation in Host-Parasite Interactions.- 1. Concepts of Metabolic Regulation and Possible Application to Host-Parasite Interactions.- 2. Assessment of Intermediary Metabolism.- 2.1 Selection of Appropriate Procedures.- 3. Compartmentation as a Regulatory Device.- 3.1 Sites of Compartmentation and Functional Roles.- 3.2 Detection of Compartmentation in vivo.- 3.3 Compartmentation in Host-Parasite Interactions.- 4. Enzymes as a Regulatory Device.- 5. Energy Charge.- 6. Pyridine Nucleotides as Regulators of Metabolism.- 7. The Pasteur Effect.- References.- 6. Modification of the Host Response—Predisposition.- 1. The Problem.- 2. Conditions Which Predispose Plants to Disease.- 2.1 Temperature.- 2.2 Humidity.- 2.3 Light.- 2.4 Chemicals.- 2.5 Tillage.- 2.6 Pruning.- 2.7 Grafting.- 2.8 Vigor.- 2.9 Prior Infection.- 2.10 Nonparasitic Diseases.- 2.11 Agronomic Practices.- 3. The Future.- References.- 7. Biotrophic Parasites in Culture.- 7.1 Growth of Biotrophic Parasites in Axenic Culture.- 1. Introduction.- 2. Culture of Rust Fungi from Uredospores.- 3. Mycelial Types Formed in Axenic Culture.- 4. Nutritional Studies.- 5. Pathogenicity of Axenic Cultures.- 6. Factors Affecting the Development of Individual Sporelings.- 7. Axenic Culture of Other Obligate Fungi.- 8. The Culture of Mycoplasma-like Organisms.- 9. Conclusions.- References.- 7.2 Growth of Biotrophic Parasites in Tissue Culture.- 1. Introduction.- 2. Plant Tissue Culture Methods.- 3. The Growth of Viruses in Tissue Culture.- 3.1 Growth in Callus Tissues.- 3.2 Production of Virus-free Plants.- 3.3 Growth in Cell Cultures.- 4. The Growth of Biotrophic Fungi in Tissue Culture.- 4.1 Growth in Callus Tissue and Suspension Cultures.- 4.2 Growth in Organ Cultures and Protoplast Cultures.- 5. The Growth of Nematodes in Tissue Culture.- 5.1 Infection of Organ Cultures.- 5.2 Infection of Callus-tissue Cultures.- 6. Conclusions.- References.- 8. Genetics of Host-Parasite Interactions.- 1. Introduction.- 2. Inheritance of Resistance and Virulence.- 2.1 Inheritance of Resistance in Flax (Linum usitatissimum) to Melampsora lini.- 2.2 Inheritance of Virulence in Melampsora lini.- 2.3 Basic Genetic Patterns of Host-Parasite Relationships.- 3. Constitutive or Adaptive Function of the Genes Controlling Specificity.- 4. Specific Interactions for Compatibility or Incompatibility.- 5. Perspective of Evolution of Different Types of Int...