VIEW ARTICLE

Etiology

A New Cercospora Leaf and Stem Disease of Subterranean Clover. R. G. Pratt, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, and Department of Plant Pathology and Weed Science, Mississippi State University, P.O. Drawer PG, Mississippi State 39762; Phytopathology 74:1152-1156. Accepted for publication 7 May 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1152.

A severe disease caused by Cercospora was observed on foliage of subterranean clover at two locations in Mississippi. The pathogen was identified as a new, host-specific form of Cercospora zebrina. Symptoms developed on susceptible cultivars of subclover 8- 10 days after leaves were inoculated with conidia under favorable conditions. Disease was most severe when plants were maintained at 25- 31 C and incubated in a saturated atmosphere for ≥72 hr following inoculation. Symptoms developed more slowly at lower temperatures and were greatly reduced with shorter periods of saturation. Pathogenicity was evaluated on 11 species of Trifolium and Medicago; severe and consistent disease symptoms developed only on subterranean and rose clovers. Among 17 cultivars of subterranean clover, 14 were highly susceptible and three were moderately to highly resistant. Field plots were effectively inoculated by applying infested debris to foliage and by transplanting infected plants from the greenhouse; infested debris gave more uniform infection. Results suggest that the new Cercospora disease could potentially reduce forage production and reseeding by subterranean clover in the southeastern United States.