X-Disease Confirmation and Distribution in Chokecherry in North Dakota. Y. H. Guo, Graduate Student, Department of Plant Sciences, North Dakota State University, Fargo 58105. J. A. Walla, Research Associate, Department of Plant Pathology; Z.-M. Cheng, Assistant Professor, Department of Plant Sciences, North Dakota State University, Fargo 58105; and I.-M. Lee, Research Plant Pathologist, USDA-ARS, PSI BARC-West, Molecular Plant Pathology Laboratory, Beltsville, MD 20705. Plant Dis. 80:95-102. Accepted for publication 27 September 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0095.

A phytoplasma was observed in diseased chokecherry plants in North Dakota by electron microscopy and identified with a phytoplasma-specific polyclonal antibody and with restriction fragment length polymorphism (RFLP) analysis of 16S ribosomal DNA (16S rDNA) sequence amplified with the nested polymerase chain reaction (PCR). The phytoplasma was partially purified directly from infected chokecherry plants for use in raising a polyclonal antibody in mice. The specificity of the polyclonal antibody against phytoplasma was shown by its reaction with diseased, but not with healthy, chokecherries upon immunofluorescence staining. Immunofluorescence staining demonstrated the chokecherry phytoplasma in North Dakota to be serologically related to phytoplasmas associated with eastern X, western X, milkweed yellows, and pigeon pea witches'-broom disease. The antibody did not react with phytoplasmas associated with ash yellows, aster yellows, elm yellows, goldenrod yellows, spirea stunt, and palm lethal yellowing. The identity as X-disease phytoplasma was supported by RFLP analysis of the amplified products obtained from the nesled-PCR by using two phytoplasma-universal primer pairs. The RFLP patterns from MseI and HpaII digestion indicated that the X-disease phytoplasma in chokecherry belongs to subgroup A in the 16S rRNA group III. The presence of X-disease symptoms, electron microscopic observation of phytoplasmas in symptomatic plants, detection with the polyclonal antibody, and detection and identification by PCR-RFLP analysis provided the first confirmation that chokecherry X-disease occurs in the Great Plains region. Chokecherry X-disease was found to be widespread in North Dakota based on positive Serological detection of X-disease phytoplasma in chokecherry samples collected throughout North Dakota. X-disease in chokecherry was also confirmed in South Dakota and in Saskatchewan, Canada.

Keyword(s): phytoplasma purification, Prunus virginiana, serology