Rhizopus Soft Rot of Euphorbia trigona. E. N. Mulrean, Junior Specialist, Department of Plant Pathology, University of California, Berkeley 94720. A. H. McCain, Extension Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 65:159-161. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-159.

Rhizopus stolonifer was consistently isolated from a rapidly advancing soft rot of Euphorbia trigona. Symptoms were reproduced on healthy E. trigona by inoculating propagation wounds with sporangiospores of R. stolonifer. Plants wounded and immediately inoculated developed symptoms within 24 hr at 16, 21, and 27 C, but no symptoms developed at 32 C. Resistance to infection at 32 C could not be directly related to the rate of wound tissue formation by the host or to adverse effects of temperature on spore germination or mycelial growth of the fungus. Nine other species of Euphorbia were tested for susceptibility to Rhizopus soft rot. Dicloran (Botran 75W) applied to E. trigona propagation wounds before inoculation completely controlled Rhizopus soft rot.