Disease Note

First Report of Amphobotrys ricini Infecting Caperonia palustris in the United States. N. G. Whitney, Texas A&M University Agricultural Research and Extension Center, Beaumont 77706. R. A. Taber, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843. Plant Dis. 70:892. Accepted for publication 25 April 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-892e.

A stem canker epidemic resulting in the complete mortality of an adult texasweed (Caperonia palustris (L.) St. Hil.) population was observed in the summer of 1984 at the Texas A&M University Agricultural Research and Extension Center in Beaumont. Texasweed is an economically important weed in rice and soybeans in the Gulf Coast area. The fungus causing the disease was isolated on potato-dextrose agar from black sclerotia embedded in the stem tissue of dead plants. In culture, the colonies are light gray and macroscopically similar to those in cultures of Botrytis. Conidiophores are long, slender, pigmented, and highly branched, with clusters of conidia at the apex of each branch. Conidia are ovoid, one-celled, and hyaline. Conidia and hyphae were inoculated into healthy texasweed stems with autoclaved toothpicks. Within 3 days, cankers were produced at inoculation sites; the cankers enlarged, girdled the stems, and killed the plants in approximately 2 wk. The fungus was reisolated from inoculated texasweed in September 1984. The causal fungus was identified as Amphobotrys ricini (Buchw.) Hennebert (2). This species causes a gray mold of castorbean (Ricinus communis L.) (1) but has not been reported on other plants in the United States until now.