CITRUS ROOTSTOCKS: THEIR CHARACTERS AND REACTIONS (an unpublished manuscript) ca. 1986 By W. P. BITTERS (1915 – 2006) Editor, digital version: Marty Nemeth, Reference Librarian, UC Riverside Science Library, retired Subject matter experts, digital version: Dr. Tracy Kahn, Curator, UC Citrus Variety Collection Dr. Robert Krueger, Curator, USDA-ARS National Clonal Germplasm Repository for Citrus & Dates Toni Siebert, Assistant Curator, UC Citrus Variety Collection ca. 1955 ca. 1970 IN MEMORIUM Willard P. Bitters Professor of Horticulture, Emeritus Riverside 1915-2006 Born in Eau Claire, Wisconsin, in June, 1915, Dr. Willard “Bill” Bitters earned his bachelor’s degree in biology from St. Norbert College and his master’s degree and Ph.D. from the University of Wisconsin. After earning his doctorate, he first worked as the superintendent of the Valley Research Farm of the University of Arizona in Yuma, and joined the Citrus Experiment Station, in Riverside in 1946 as a Horticulturist. In 1961, Dr. Bitters became a Professor in the newly established University of California-Riverside. His initial assignment was to work on horticultural aspects of tristeza, a serious vector-transmitted virus disease which threatened to destroy California citrus orchards. Tristeza was already in California and spreading in 1946. At that time most citrus trees in California were grafted on a rootstock that was known to be susceptible to tristeza. Dr. Bill Bitters was responsible for screening of over 500 cultivars to determine which rootstock-scion combinations were resistant to this disease and yet possessed suitable horticultural characteristics. Of the 500 screened, most were susceptible, but several successful ones were selected and released to the industry. Among these were ‘Troyer’ citrange and Citrus macrophylla, which continue to be important rootstocks worldwide. The industry greatly benefited by such releases. Another important contribution was his developmental work with ‘Flying Dragon’ trifoliate rootstock, which is able to dwarf most standard cultivars by 90 percent, making them easier to harvest. Perhaps Dr Bitters’ most important contribution was his work with the Citrus Variety Collection. Herbert John Webber, the first director of the Citrus Experiment Station, had initiated and overseen the Citrus Variety Collection up until his death in 1944. When Dr. Bitters became the curator of the collection in 1947, it had been somewhat neglected. Dr. Bitters was instrumental in increasing the number of accessions in the collection from 600 to 1200. This collection is still recognized as one the major collections of citrus genetic resources in the world. During his time working with the Citrus Variety Collection, Dr. Bitters traveled extensively throughout the citrus growing regions of the world. He became known as a world authority on citrus scion and rootstock cultivars, and was well versed in many other areas of citriculture. Dr. Bitters was the author of 99 publications of significant benefit to citrus researchers and growers throughout the world. In 1967, Dr. Bitters received the Annual Citrograph Award in recognition of his many outstanding contributions resulting in the utilization of rootstock and scion varieties that produce improved tree growth and fruit quality. ii After his retirement in 1982, Dr. Bitters continued to work with other University of California Riverside researchers to improve the quality of the Citrus Variety Collection, advise others working in citriculture, and to serve the public through the University of California Cooperative Extension Master Gardeners Program. He was a member of many academic organizations, including the American Society of Horticultural Science, the International Society of Citriculture, the Japanese Society of Horticultural Science, and the California Lemon’s Men’s Club. Tracy L. Kahn Carol J. Lovatt Robert R. Krueger Jodie S. Holt iii EDITOR’S PREFACE, DIGITAL VERSION Substance and Context The Citrus Experiment Station, established in 1907, is the world-eminent citrus research center, and its publications were consulted by citrus growers and scientists everywhere. The Citrus Experiment Station undertook a revision of The Citrus Industry, originally published 1943-1948, in the early 1960’s. This was to be a comprehensive landmark work that included all the Citrus Experiment Station research up to that time, as well as research from other citrus scientists from around the world, in all areas of citriculture. Dr. W. P. Bitters (1915-2006) began his career at the Citrus Experiment Station in 1946. His assignment was to study citrus rootstocks, their disease resistance, and their graft compatibilities with various commercial citrus varieties. Dr. Bitters undertook a series of comprehensive experiments that involved hundreds of trees, at three different locations in California, and lasted more than 20 years. This was truly a historic and landmark undertaking, never done before, and never repeated. It is still considered the seminal research on citrus rootstocks. Over the years Dr. Bitters became renowned as a world authority on citrus rootstocks and many other areas of citriculture. The published results from his experiments, and personal consultation until his death, form the basis of all current experimentation on citrus rootstocks. A chapter on citrus rootstocks by Dr. Bitters was to be part of the 5th volume of the The Citrus Industry, revised edition, 1967-1989. Ultimately the chapter was not included, and efforts to publish it as a separate volume were not successful. After Dr. Bitters’ death in 2006, a typescript draft of this chapter was found among his papers. It was determined that this draft was the latest. Dr. Bitters ceased work on the manuscript ca. 1986. This monograph is a comprehensive work on citrus rootstocks, not only reporting the results of Dr. Bitters’ landmark experiments and research, but aggregating and correlating those results with all other known experiments on citrus rootstocks from all over the world, a truly landmark work. The bibliography alone is a significant historical record of citrus rootstock research from every part of the world, and includes many references to published materials that have rarely, if ever, been referenced elsewhere. The monograph also includes unpublished research results from Dr. Bitters work, and from various growers’ experiments, observations, and experiences. Dr. Tracy Kahn, Curator of the UC Citrus Variety Collection and longtime friend and colleague of Dr. Bitters, suggested digitizing the manuscript. Permission to publish an electronic edition of this unpublished monograph was granted by Dr. Bitters in his lifetime. Subsequently, Dr. Kahn received permission from Dr. Bitters’ heirs to publish a digital version. She brought the manuscript to Marty Nemeth, a librarian retired from the UC Riverside Science Library (now the Orbach Science Library), who was responsible for previous digitization efforts. Condition of the Manuscript The manuscript is a typed carbon (2 copies), double-spaced, on yellow paper. It consists of 17 headed sections, including an introduction and a bibliography, in 262 consecutively numbered pages with no hand-written annotations, so there are no questions about how the material should be organized. Tables are included as part of the text. There are some blank spaces and lines, indicating an intent to complete the thought or reference at a later date. In addition, some text references lack dates and/or lack a corresponding entry in the bibliography. There are references to figures, but no images in any format are attached or specifically iv designated for inclusion. Some sections were added subsequent to the main portion, and are not as polished, but nonetheless contain invaluable information and unpublished data from Dr. Bitters’ experiments and observations. Editorial Practices In general, the editorial guidelines used were those of copy editing only. All editorial annotations are in italics within brackets. Copy editing: Copy editing guidelines: all spelling errors have been corrected, without annotation; punctuation was inserted, where appropriate, without annotation; occasionally, if a word was needed to clarify the meaning of a sentence, it was inserted without annotation (beyond that no rewriting was done); the author’s phrasing, word selection, and general style were not altered and no annotations of “[sic]” were made; blank lines in the manuscript, which were left to indicate the intent to complete the sentence or thought at a later editing, were indicated by an explanatory annotation; the numerous textual bibliographic references to unpublished materials, many without date, were not included in the bibliography because there is insufficient information to identify or verify them. Fact checking: . All citrus names, geographic areas, technical terms, etc were checked and have been corrected, without annotation. All references were verified; corrections were made where necessary, without annotation. References in the text for which there are no dates (just authors) and/or for which there are no corresponding items in the bibliography, were identified, where possible, by correlating information in the manuscript with the referenced item in hand, and the verified items were added to the bibliography without annotation. Illustrative materials: . Some photographic slides, among the hundreds that were among Dr. Bitters’ papers, were identified as corresponding to references in the manuscript; these are included