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Ecology and Epidemiology

Characterization of the Periconia circinata Population in a Milo Disease Nursery. G. N. Odvody, Former Graduate Assistant, Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583; L. D. Dunkle(2), and L. K. Edmunds(3). (2)Associate Professor, Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583; (3)Research Plant Pathologist, United States Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, Kansas State University, Manhattan KS 66506. Phytopathology 67:1485-1489. Accepted for publication 23 May 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1485.

The toxin-producing ability and pathogenicity of isolates of Periconia circinata isolated from soil and sorghum in a milo disease nursery were investigated. In culture, 13% of isolates from soil, 34% from roots of susceptible sorghums, and none from resistant sorghums produced a toxin that was active against susceptible sorghum seedlings. None of the isolates produced a toxin with detectable activity against sorghum genotypes considered to be resistant. Conidia of P. circinata persisted in field soil and, in laboratory studies, functioned as infective propagules. Conidia from both toxin-producing and non-toxin-producing isolates germinated on host roots, formed apparent infection structures, and incited cortical lesions on roots of susceptible and resistant sorghums. However, extensive vascular infections and eventual death occurred only on susceptible sorghums inoculated with toxin-producing isolates. Non-toxin-producing isolates of P. circinata were weak parasites of sorghum in the laboratory. The possible origin and pathogenic potential of P. circinata are discussed.

Additional keywords: root exudates, host-specific toxin, pathotoxin, root rot.