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Discussion: Fastidious Prokaryotes as Plant Pathogens

Current Status of the Etiology of Pear Decline. Boligala C. Raju, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Yoder Bros., Inc., P.O. Box 68, Alva, FL 33920; George Nyland(2), and Alexander H. Purcell(3). (2)Department of Plant Pathology, University of California, Davis 95616; (3)Department of Entomological Sciences, University of California, Berkeley 94720. Phytopathology 73:350-353. Accepted for publication 29 July 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-350.

Samples from diseased pear were collected from each of 10 trees from June 1980 to April 1981. Pear psylla were also collected from pear at the same time. Helical and motile spiroplasmas were isolated from two of 10 trees four times in 330 isolation attempts. Spiroplasma also were isolated from psylla collected during early December 1980, but not from 30 other collections made at other times of the year. No spiroplasma was isolated from healthy pear grown from seed, or from healthy or diseased periwinkle. The isolates from pear were serologically and culturally indistinguishable from Spiroplasma citri. No transmission to healthy pear occurred when pear psylla were injected with these spiroplasma isolates. No symptoms were seen in pear and periwinkle on which field-collected psylla were caged. Dienes' stain did not clearly distinguish healthy from pear decline-affected pear tissue. An infectious agent has been transmitted via dodder from pear with pear decline symptoms to periwinkle. Diseased periwinkle could be distinguished from healthy with Dienes' stain. Based on inconsistent isolations of spiroplasmas from pears and on results from pathogenicity studies, we conclude that the spiroplasma isolated from pear is not the causal agent of pear decline.