The Plant Root and the Rhizosphere was a major topical feature of the first International Symposium on Factors Determining the Behavior of Plant Pathogens in Soil held at the University of California, Berkeley in 1963. The symposium was edited by K. F. Baker and W. C. Snyder and published under the title Ecology of Soil-Borne Plant Pathogens. Since that time, several other international efforts, either on the root-soil interface specifically or on topics relating to the root environment, have provided"a wealth of valuable information basic to promoting the culture of healthier, more productive plants. For the writing of this book, inspiration has come, in large part, from 10 years of cooperative rhizosphere research in association with leading scientists participating in a regional effort within the southern United States. We have attempted to bring together in this work the major aspects of rhizosphere research and the principles of rhizosphere ecology for the benefit of developing young scientists and technologists, as well as for the established professional researcher and teacher. A prime objective and hope is that this volume might generate ideas that will bring forth new approaches and methodology leading to further advances in our understanding of rhizosphere interactions and their implications for agriculture. ' Because of the enormous complexity of the chemical, physical, and microbiological environment of roots, the methods used by various workers are rarely standardized, but must be devised or modified for each experiment.

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1 Introduction.- 1.1 Definitions and Historical.- 1.2 The Root Environment.- 1.3 Significance and Purpose of Rhizosphere Investigations.- 2 The Structure and Function of Roots.- 2.1 Introduction.- 2.2 Root Morphology.- 2.3 Root Structure.- 2.4 Root Physiology.- 2.5 The Root-Soil Boundary.- 2.6 Root Exudation.- 3 Root Exudates.- 3.1 Introduction.- 3.2 Methods of Collection and Analysis.- 3.3 Qualitative and Quantitative Nature of Exudates.- 3.4 Sites of Exudate Release.- 3.5 Factors Affecting Exudation.- 3.6 Sloughed Organic Matter.- 4 Rhizosphere Populations.- 4.1 Introduction.- 4.2 Isolation and Enumeration of Microorganisms.- 4.3 Populations of the Microflora.- 4.4 Qualitative Changes in the Microflora.- 4.5 Factors Affecting Populations of the Microflora.- 4.6 Populations of the Rhizosphere Fauna.- 5 Microbial Interactions.- 5.1 Introduction.- 5.2 Growth-Promoting Interactions.- 5.3 Growth-Inhibiting Relationships (Antagonism).- 6 Rhizosphere in Relation to Plant Nutrition and Growth.- 6.1 Introduction.- 6.2 Nutrient Availability and Uptake.- 6.3 Nonsymbiotic Nitrogen Fixation.- 6.4 Symbiotic Relationships.- 6.5 Microbial Metabolites.- 6.6 Plant Effects on Other Plants.- 7 Rhizosphere Relation to Plant Disease.- 7.1 Introduction.- 7.2 Pathogen Populations.- 7.3 Growth and Survival in the Rhizosphere.- 7.4 Pathogenesis.- 7.5 Pathogenesis Without Parasitism.- 7.6 Disease Control.- 8 Current Trends and Projected Emphasis.- 8.1 General Overview.- 8.2 Status of the Technology.- 8.3 Relating to Plant Growth.- 8.4 Opportunities in Plant Pathology.- 8.5 Focus: The Rhizosphere and Crop Production.- References.