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Chester N. Roistacher has been specializing in the detection and diagnosis of citrus virus and virus-like diseases for many years. During this time, he has developed a general philosophy on indexing that has led to the concept of the plant laboratory as a most important means of detecting several of the citrus virus and virus-like diseases.

The International Organization of Citrus Virologists, from its very inception, has had a history of international cooperation for the study, detection and ultimate elimination of citrus virus and virus-like diseases. Since its foundation over 30 years ago, one predominant principle has emerged: the problems related to citrus virology in one country, no matter how remote or distant that country may be, are similar to the problems in any other citrusgrowing country. Thus, the findings of workers in one institute are applicable and helpful to workers in another. This handbook exemplifies the spirit of cooperation that has prevailed in our organization in the sharing of knowledge among citrus scientists.

The importance of the practical applications of the material of this handbook might best be appreciated by relating the story of my own meeting and personal relationship with the author. I first met Chet Roistacher in1972 while working at the University of California in Riverside, attempting to define and improve the shoot-tip grafting method and to understand its mechanisms and principles. I had accumulated in test-tubes many hundreds of small plants. I had worked very hard during many long and late hours under a hood and using a microscope in cutting extremely small tips from their microscopic shoot apices, carefully grafting them to small, toothpicksized seedlings, and then putting the grafted seedlings back into the test-tubes. I was now ready to transplant these many small growing plants to the soil. However, past experience with other greenhouses led me to fear that, once these small plants were removed from their sterile and secure homes in the test-tubes, they might easily be destroyed by phytophthora infection, poor soil or neglect. At this point I was introduced to Chet at the Rubidoux greenhouse, and he enthusiastically explained to me many of the concepts and principles now detailed in this handbook. Most important, he gave me hope and confidence that my many hard months of research would not be destroyed and we would have success with survival of my test-tube plants.

In truth, we achieved over 95 percent success in survival and growth of the plants which had been successfully transplanted to the UC soil mixture. We watched them grow from small, fragile plants just after the shock of transplanting to mature, vigorous plants in the greenhouse, and ultimately to fruiting trees in the field. I became a convert to this system of plant growth, which recognized the extreme importance of sanitation, nutrient balance, a good soil mixture with balanced fertilization plus responsible care. We later went on to index all of these shoot-tip grafted plants, and I was able to see and study at first hand the importance of good plants for the detection of citrus viruses. I also came to appreciate better the concept of the plant laboratory. I copied the formulae and concepts learned at Riverside and brought them back to Spain. At my request, Chet came to Spain in1975 to teach and to see if those principles, which worked so well at Riverside, would work equally well in Valencia. They did!

Chet has always enthusiastically shared his knowledge with his many visitors from all over the world who go to the University of California at Riverside, in his many trips to most citrus-growing areas, and with all the members of the International Organization of Citrus Virologists. At the meetings of this organization, Chet has made many important contributions not only with his formal presentations of papers but also in his long discussions with everybody on the concepts and procedures for indexing citrus virus diseases.

Detection and diagnosis of graft-transmissible diseases of citrus is a most significant contribution to the citrus industries of all countries and for the advancement of citrus virus research. I feel it will be extensively used, both by new scientists entering this field and by scientists with wide experience in citrus virus diseases.

Finally, on behalf of the IOCV, I wish to acknowledge the wisdom and foresight of FAO in stimulating and supporting the publication of this handbook.

Luis Navarro
International Organization of Citrus Virologists

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