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.

Contenu

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 Incepti…