Disease Note

Dichotomophthora portulacae Causing Black Stem Rot on Common Purslane in Texas. J. K. Mitchell, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. Plant Dis. 70:603. Accepted for publication 23 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-603b.

Dichotomophthora portulacae Mehrlich & Fitz. ex M. B. Ellis, the causal agent of black stem rot on common purslane (Portulaca oleracea L.), was isolated from diseased plants in Burleson County, Texas, in 1984. This is the first report of this pathogen in the southern United States. Infected plants were completely defoliated and the blackened stems had numerous constrictions. Cuttings from nondiseased purslane plants were grown to a height of 16 cm in a greenhouse, then sprayed to runoff with a suspension of 5 × 10⁵ spores per milliliter in Tween 20 (6 drops to 1 L of water). The plants were completely defoliated within 20 hr after placement in a dew-deposition chamber at 25 C, and the stems collapsed 48 hr later. Carpetweed (Mollugo verticillata L.) plants developed chlorotic flecks when inoculated with the pathogen by the same technique. The rapid death of inoculated purslane plants exemplifies the potential of this fungus as a bioherbicide.