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Quantification of Plant Pathogenic Spiroplasmas from Infected Plants. J. W. Kloepper, Former assistant professor, Plant Pathology Department, University of California, Berkeley 94720, Current address of senior author: research plant pathologist, Advanced Genetic Sciences, Inc., P.O. Box 1373, Manhattan, KS 66502; D. G. Garrott(2), and G. N. Oldfield(3). (2)Staff Research Associate, Plant Pathology Department, University of California, Berkeley 94720; (3)Research entomologist, USDA Boyden Entomology Lab, Riverside, CA 92521. Phytopathology 72:577-581. Accepted for publication 1 September 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-577.

Quantification of spiroplasmas in host plant tissue was accomplished by centrifuging samples to remove possible spiroplasma inhibitors and plating the samples directly on a solid medium. Population estimates varied less than one log unit among different replications of a given sample and therefore, populations were determined by taking the average of four to six replications per sample. Populations of spiroplasmas ranged from a minimum detectable number of 50 colony-forming units per gram (cfu/g) to a maximum of 3.1 106 in foliage of celery, periwinkle, orange, corn, and plantago in the greenhouse. Populations in plants fed on by leafhoppers injected with Spiroplasma citri originally isolated from cherry with Green Valley X disease averaged 6.0 105 cfu/g but only averaged 50 cfu/g when the leafhoppers were fed on the cherry and allowed to transmit without injection to indicator plants. Populations of S. citri and the corn stunt spiroplasma were approximately 1 log unit lower in roots than in petioles of greenhouse plants. Spiroplasmas were present at detectable levels in all ages of host plants; however, the populations averaged 1.01.5 log units less in old leaves than in young leaves. Populations in field-grown broccoli naturally infected with S. citri averaged 4.8 105, while spiroplasma populations averaged 2.1 105 in plants infected with both S. citri and nonhelical vinca virescence mycoplasmalike organism (MLO). Electron micrographs of thick longitudinal sections revealed the presence of two distinct organisms: one filamentous and helical, the other globular in plants infected with both S. citri and the vinca virescence MLO. Only filamentous helical organisms were seen in plants infected with S. citri.