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Disease Detection and Losses

Isolation of a Potyvirus from Declining Clones of Populus. R. R. Martin, Former research assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706, Present address: Department of Botany and Plant Pathology, Rm. 1067, Oregon State University, Corvallis 97331; J. G. Berbee(2), and J. O. Omuemu(3). (2)(3)Professor, and former research assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706, (3)Present address: Ministry of Agriculture and Natural Resources, Benin City, Nigeria. Phytopathology 72:1158-1162. Accepted for publication 11 January 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1158.

A virus was transmitted mechanically to herbaceous indicator plants from six declining Populus euramericana clones, two declining Populus tremuloides clones, and two declining Populus grandidentata clones. The virus induced local lesions on inoculated Chenopodium quinoa and both local lesions and systemic symptoms on Phaseolus vulgaris and Vigna unguiculata (cowpea). Usually less than 10% of the herbaceous indicator plants inoculated with leaf sap from declining poplars became infected. When inoculated with leaf sap of infected cowpea, P. tremuloides seedlings developed chlorotic and necrotic leaf spot symptoms similar to those observed on declining poplars. The virus was transmitted back to cowpea from inoculated symptomatic but not asymptomatic seedlings of P. tremuloides. Electron microscopy of four representative isolates revealed flexuous rod-shaped virus particles (with a modal length of 800810 nm) in sap from cowpea leaves and associated potyvirus-induced inclusions in thin sections of cowpea leaf tissue. All four isolates had a thermal inactivation point between 58 and 60 C, a dilution end point of 104 in cowpea leaf sap, a longevity in vitro of 24 hr at 22 C, and identical host ranges. This virus is a member of subdivision I of the potyvirus group. It can be differentiated from other viruses in that group by particle length, host range, and symptomatology.

Additional keywords: aspen decline.