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Discussion: Fastidious Prokaryotes as Plant Pathogens

Evidence for a Mixed Infection of Spiroplasmas and Nonhelical Mycoplasmalike Organisms in Cherry with X-Disease. J. W. Kloepper, Former assistant professor, Department of Plant Pathology, University of California, Berkeley 94720, Current address of senior author: Advanced Genetic Sciences, Inc., P.O. Box 1373, Manhattan, KS 66502; D. G. Garrott, staff research associate, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 73:357-360. Accepted for publication 29 July 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-357.

Spiroplasmas were isolated from 4 and 5% of total samples from individual Green Valley X-diseased cherry trees in two orchards in San Joaquin County, CA, in 1980; however, 53 and 78% of diseased trees in the orchards yielded spiroplasmas at some time of the year. In 1981, spiroplasmas were isolated from 40% of diseased trees and 60% of healthy trees in one orchard. All isolates were obtained during a 2- to 3-wk period shortly before fruit maturity; subsequent attempts to isolate spiroplasmas from the same trees were negative. The isolated spiroplasmas were serologically indistinguishable from Spiroplasma citri. Mycoplasmalike organisms (MLOs) were detected in high numbers in electron micrographs of phloem from X-diseased trees throughout the season, including times when no spiroplasmas were isolated. MLOs from diseased cherry were nonhelical as revealed with high voltage and standard electron microscopy. Helical MLOs were detected in sections of celery inoculated via leafhoppers (Colladonus montanus) with spiroplasmas isolated from X-diseased cherry. The results suggest that the X-disease agent is a noncultivatable, nonhelical MLO rather than a spiroplasma, and that both symptomless and X-diseased cherry in California are occasionally infected with S. citri.