Soilborne Pathogens of Euphorbia lathyris: Macrophomina phaseolina, Pythium aphanidermatum, and Rhizoctonia solani. Deborah J. Young, Research Assistant, Department of Plant Pathology, University of Arizona, Tucson 85721. S. M. Alcorn, Professor, Department of Plant Pathology, University of Arizona, Tucson 85721. Plant Dis. 66:236-238. Accepted for publication 4 June 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-236.

Macrophomina phaseolina, Rhizoctonia solani, and Pythium aphanidermatum were isolated from Euphorbia lathyris grown in fields near Tucson, AZ. R. solani occurred as a damping-off organism in the fall. During the summer, M. phaseolina was a major pathogen, particularly infecting plants at least several months of age; sclerotia frequently formed on roots and in pith tissues. Some plants infected with M. phaseolina were growing in an area newly cleared of native desert vegetation. It was also isolated from E. lathyris field plants dying during the summer in western Arizona and Utah. Pythium aphanidermatum infected seeds, seedlings, and mature plants in laboratory and greenhouse tests. Although P. aphanidermatum was infrequently isolated from field plants in Arizona, it was a major pathogen of greenhouse plants growing at high temperatures in nonsterile soil. Fusarium spp. were frequently isolated from root lesions, but their role as pathogens is not yet known.

Keyword(s): gopher plants, hydrocarbon source.