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Detection of Mycoplasmalike Organisms in Infected Blueberry Cultivars by the DAPI Technique. Ulrike Schaper, Research Associate, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. R. H. Converse, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 69:193-196. Accepted for publication 25 September 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-193.

Coded samples from stunt-infected and healthy blueberry plants were evaluated for the presence of mycoplasmalike organisms (MLOs) by comparing two histological techniques. By the DAPI (4,6-diamidino-2-phenylindole) technique with root tissue, MLOs were directly detected, whereas by the aniline blue (AB) technique with petiole samples, MLOs were indirectly monitored by detecting the resulting excess callose in sieve tubes. With DAPI, 24 of 25 infected and 25 of 25 healthy root samples were correctly evaluated. With AB, 19 of 25 infected and 10 of 25 healthy petiole samples were correctly evaluated. MLOs were observed by electron microscopy in root samples from one stunt-infected, DAPI-positive plant but not in root samples from one known healthy, DAPI-negative blueberry plant. Root samples from clones of several symptomless highbush blueberry cultivars were classified as MLO-positive by the DAPI technique. Petiole and stem samples from these same plants were rated negative by the DAPI test.