PREFACE

      For two decades The Citrus Industry, published in two volumes, has been the standard reference work on the biology and culture of citrus throughout the world.   It was one of the first works to deal comprehensively with a single crop, and it has had an enormous impact on the technology of citrus production.
      The first volume, History, Botany, and Breeding, edited by H. J. Webber and L. D. Batchelor, was published by the University of California Press in 1943.   The supply was soon exhausted and a second printing of that initial volume was published in 1946, followed by a third printing in 1948.   A larger printing of the second volume, Production of the Crop, edited by L. D. Batchelor and H. J. Webber, was published in 1948 by the University of California Press.   Thus, as this is written, the information in the original volumes is somewhere between twenty and twenty-five years old, if one allows about two years for review, revision, editing, and printing.
      During the past twenty-five years, the production of citrus in the United States has almost doubled (there are now more citrus trees in this country than all other fruit trees combined).   Similar expansions in citrus production have taken place in many of the other principal citrus-growing countries of the world.   During this period, a parallel increase has occurred in the tempo of citrus research.   In the United States and some other countries, the two decades following World War II were years of unprecedented expansion of the support for scientific research and development in general.   The forces of increased production and accelerated research have greatly stimulated not only the development of new citrus technology, but also the harvest of new, basic, scientific knowledge.
      Many sections of the original volumes of The Citrus Industry have been rendered obsolete.   Some new areas of basic knowledge and technology have arisen that were merely touched upon, or not even considered in the original volumes.   Thus, by the time that supplies of the original volumes became exhausted (about 1961), it was clear that a substantial revision and expansion was required, rather than further printings of unrevised editions.   Yielding to pressures from Dean A. M. Boyce and other colleagues, I agreed to serve as editor for a new, revised edition.   Accordingly, Citrus Research Center and Agricultural Experiment Station Project 2015 was initiated July 21, 1961 for "Revision of the publications, The Citrus Industry, Volumes I and II."
      Material covered in the original Volume I has been expanded to such an extent that it was necessary to divide it into two volumes.   Thus, distribution, botany, and varieties.   Revised Volume II will encompass morphology and anatomy, physiology, climatic influences, mineral nutrition, genetics, breeding, and seed reproduction.   Volume III will deal with the technology of citrus culture.   It will include sections on rootstocks, fertilization, leaf analysis, soil management, planning and planting an orchard, propagation, pruning, thinning, girdling, plant growth regulators, frost protection, irrigation, and chemical weed control.   Volume IV of this new edition of The Citrus Industry will cover pests and diseases of citrus.   This final volume will include sections on the biology and control of seedbed, nursery, and orchard diseases, virus diseases, post-harvest diseases, chewing insects, mites, scales, thrips, aphids, snails, nematodes, and rodents.   Other chapters will deal with the replant problem, biological control of insects, budwood certification, and quarantine problems.
      This is a University of California publication, and most of the senior authors of chapters in this four-volume series are members of the staff of the University of California.   The majority are closely affiliated with the Citrus Research Center and Agricultural Experiment Station at Riverside.   The general outlook and treatment of subject matter in some chapters for this reason tends inevitably at times to reflect a somewhat regional outlook.
      However, increased published information from other areas of the world and improved transportation and communications have provided the authors with a broader base of information and experience than was available to the contributors to the original volumes.   A special effort was also made to expand coverage of the technology of citrus production by stimulating authors to visit other important producing areas and, in a few cases, to collaborate with key colleagues affiliated with the U. S. Department of Agriculture or the University of Florida.   In the technology sections, an effort was made to focus on basic principles underlying practices and to devote less emphasis to details of current practices, which rapidly become outdated anyway.
      In preparing some of the topics included in the original volumes, authors were requested either to revised material or rewrite completely, depending on the extent of development of knowledge and technology in the areas since the previous publications.   Most of the chapters in the four volumes of this new edition have been completely rewritten.   A few of the chapters in Volumes I and II, however, have been revised, reflecting areas in which advances have been less rapid in the past two decades.
      On some subjects, where it was obvious that considerable advances had taken place, topics previously covered in one chapter were subdivided into two or more chapters to provide better coverage and, in a few instances, to take advantage of the special competence of certain authors.   Relatively new areas of technology, judged to be worthy of separate new chapters, were assigned to the most competent authorities available.   All authors were requested to prepare a comprehensive review, evaluation, and synthesis of knowledge on their assigned subject with the objective of providing a reference work useful not only to their colleagues in the research and teaching fields, but also to students, technical advisors, intelligent growers, and others having an interest in the citrus industry.
      The four chapters in this first revised volume are all concerned with topics covered in Volume I of the original publication.   It seems appropriate to mention briefly some of the major changes or revisions in the material presented here.
      In Chapter 1, which deals with the history of citrus culture, minor inaccuracies have been corrected that were brought to light by recent research.   The scholarly findings of Tolkowsky, Isaac, Andrews, and others, bearing on the dates and routes of introduction of the various citrus species to the Mediterranean and elsewhere, have been integrated into the text.   Brief sections on the early history of citrus research and on recent developments in the citrus industry have been added.
      At the time H. J. Webber prepared his original chapter, "The Commercial Citrus Regions of the World," statistical and other information on citrus culture was quite limited in all but a few of the citrus-growing countries.   The much extended treatment in Chapter 2 by J. Henry Burke provides information on many of the smaller but significant citrus-growing countries.   This improved coverage was made possible by better statistical reporting, reinforced by Burke’s first-hand surveys in most of the citrus areas of the free world during the period from 1948 to 1965.
      The material presented in Chapter 3, "The Botany of Citrus and Its Wild Relatives of the Orange Subfamily," has been reprinted without major revisions.   In reviewing it, P. C. Reece added some material from pertinent recent references although some recent progress or otherwise inconclusive reports were omitted.   The discussion on the Citrus species concept was strengthened in the light of modern theories.   Reece also added a very useful detailed tabular comparison of the major systems of classification within the genus Citrus.   However, W. T. Swingle's original taxonomic system remains intact, reflecting in part the lack of support for this important area of research in the past two decades.   Editorial changes included the correction of extensive bibliographical omissions, the addition of improved or new illustrations, modernization of the synonymy, and incorporation as far as possible of the recommendations of the 1956 International Code of Botanical Nomenclature and the 1961 International Code of Nomenclature for Cultivated Plants.
      The scope of treatment of the "Cultivated Varieties of Citrus" considered in H. J. Webber's original chapter has been greatly expanded by R. W. Hodgson in his completely new Chapter 4, "Horticultural Varieties of Citrus."   A far more comprehensive coverage was attempted of both the commercial varieties grown in the United States and of those grown in the major citrus producing countries around the world.   Thus, descriptions of about 350 citrus varieties are included in Hodgson's treatment, while Webber described only about 200 varieties.   In addition, Hodgson has given more emphasis to the horticultural characteristics of varieties.
      The system of taxonomic classification followed by R. W. Hodgson is that of T. Tanaka rather than that presented by W. T. Swingle in Chapter 3.   The Tanaka system is based largely on a pragmatic, utilitarian viewpoint, while Swingle attempts to base his system primarily on genetic relationships.   Both viewpoints have validity, considering the present status of knowledge on this problem.   Thus, no attempt is made to reconcile these divergent viewpoints in this volume.   Indeed, they reflect the current situation in citrus literature.   Hopefully, future research will provide greater insight into the species problem in citrus and ultimately a generally accepted system of classification will evolve.
      I am greatly indebted to the revising authors of the chapters in this volume for their wholehearted cooperation and forbearance throughout the always time-consuming and often tedious or even downright exasperating process of progressing from the first submitted draft through numerous reviews, revisions, "final" editings, and proofings.   All who were consulted in the review and editing of the manuscripts or who contributed in other ways cannot be mentioned here: the list would be long and incomplete.   However, I would be remiss if I did not list those who graciously submitted to unreasonable demands on their time and patience in assisting with the preparation of this first volume for publication.
      Those who were most generous and helpful in reviewing parts of the text dealing with their particular specialties and fields of research include: Willard P. Bitters, James W. Cameron, John B. Carpenter, William C. Cooper, Joseph R. Furr, Robert G. Platt, Herman J. Reitz, and Robert K. Soost.   A number of persons assisted greatly in solving technical problems, often providing specific data and information that was extremely useful.   These consultants include: Mildred E. Mathias, Edmond C. Calavan, Glenn E. Carman, Homer D. Chapman, Harold J. Compere, Robert H. Hilgeman, Leo J. Klotz, L. Carl Knorr, Edward O. Olson, Rainer W. Scora, O. T. Van Niekerk, Frank C. Vasek, Harold F. Yates, and Ralph T. Brown.
      I wish to express my thanks for the efficient and tireless assistance given by Kathryn Forrest and the staff of the Agricultural Library, Citrus Research Center and Agricultural Experiment Station, and to Roy L. Kidman and the staff of the Library of the University of California at Riverside.
      Photographs of H. J. Webber and W. T. Swingle for the dedicatory pages were furnished by Fera Webber Shear and Maude K. Swingle, who were also helpful in supplying biographical material on these two pioneers of the citrus industry.
      Finally, gratitude is expressed for the editing advice and assistance on publication problems given by William W. Paul, manager of Agricultural Publications, and Lucy G. Lawrence of his editing staff.   Assistance in the preparation of illustrations and in literature searches was given by Earl S. Morton.

Walter Reuther
Riverside, California
June, 1967