VIEW ARTICLE

Effect of Soil Solution and Two Soil Pseudomonads on Sporangium Production by Phytophthora cinnamomi. W. A. Ayers, Microbiologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; G. A. Zentmyer, Professor of Plant Pathology, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 61:1188-1193. Accepted for publication 6 May 1971. DOI: 10.1094/Phyto-61-1188.

Agar-mycelial discs and washed mycelial mats of Phytophthora cinnamomi produced a few sporangia, within 24 hr, when incubated at 24 C in a sterile mineral salts solution or in autoclaved soil extracts. Nonsterile soil extracts and solutions containing two Pseudomonas isolates from soil induced the gradual development of greater numbers of sporangia over a longer period than did sterile solutions. The bacterial isolates synergistically stimulated formation of sporangia. One- and 2-day-old mats, but not 5-day-old mats, formed sporangia under axenic conditions; young mats also formed sporangia at a more rapid rate than did older mats in nonsterile soil extract. Forced aeration enhanced production of sporangia under both axenic and nonsterile conditions. Glucose at 10 to 1,000 ppm or glutamic acid at 100 ppm inhibited production of sporangia under axenic conditions, and delayed the onset of sporangium production in nonsterile solutions. The suppressing effect of nutrients appeared to be overcome by the bacterial isolates and by microorganisms in nonsterile soil extract.