Induction of sporangia in Phytophthora cinnamomi by a substance from bacteria and soil

Abstract

Production of sporangia of Phytophthora cinnamomi on agar–mycelial disks in a mineral salts solution was induced by extracts of a soil pseudomonad. Acetone extracts of soil and of mixed populations of microorganisms from soil solution also stimulated the formation of these asexual reproductive structures. Active extracts stimulated sporangium production in aqueous dilutions as high as 10−9. Some extracts of the bacterium were less active at dilutions above or below a certain optimum concentration range. The unidentified, active substance was characterized as a nonvolatile, polar, heat-stable compound that is soluble in water and several organic solvents. Salts of Ca, Mg, K, and Fe in the suspending medium favored a limited production of sporangia in the absence of active substance, and abundant sporangia in its presence. Ca2+was essential for maximum response. The substance was detected by bioassay on paper and thin-layer chromatograms, and it was obtained partially purified.