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Etiology

Detection of Multiple Phytoplasmas in Perennial Fruit Trees with Decline Symptoms in Italy. I. -M. Lee, Molecular Plant Pathology Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705; A. Bertaccini(2), M. Vibio(3), and D. E. Gundersen(5). (2)(3)Istituto di Patologia Vegetale, UniversitÓ degli Studi, Bologna, Italy; (4)Molecular Plant Pathology Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705. Phytopathology 85:728-735. Accepted for publication 6 April 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-728.

Nested polymerase chain reaction assays with two universal and four phytoplasma (formerly called mycoplasmalike organism) 16S rRNA group-specific primer pairs were employed to investigate etiologies of diseases associated with pear (decline), plum (leptonecrosis), nectarine (chlorotic leaf roll), and apricot (chlorotic leaf roll and decline) fruit crops grown in northern Italy. Restriction fragment length polymorphism analyses of phytoplasma 16S rDNA sequences amplified with various combinations of these primer pairs revealed that two to four distinct types of phytoplasmas affiliated with phytoplasma 16S rRNA group I (aster yellows phytoplasma and related strains), group III (peach X-disease and related phytoplasmas), group V (elm yellows phytoplasma and related strains), and group X (apple proliferation and related phytoplasmas) were associated with most diseases. Predominant phytoplasma strains associated with pear decline, apricot chlorotic leaf roll, and plum leptonecrosis were identified as members of group X (subgroups A and B). Phytoplasma strains associated with nectarine chlorotic leaf roll were members of group I. Minor phytoplasma strains (one or more distinct types) were also detected in each infected plant, except for those affected by apricot decline.