Culture media and sources of nitrogen promoting the formation of stromata and ascocarps inPetromyces alliaceus(AspergillussectionFlavi)

Abstract

Petromyces alliaceus Malloch and Cain is the only known sexually reproducing fungus classified in Asper gillus section Flavi. The goal of this research was to identify culture media and sources of nitrogen that best support the formation of stromata with ascocarps. Three cultures of P. alliaceus isolated from crop field soils were grown on selected agar media in Petri dishes for 7 months at 30 °C in darkness. The largest numbers of stromata were recorded for cultures grown on Czapek's agar (CZA) and a mixed cereal agar (MCA), while the percentage of stromata containing ascocarps was greatest (P ≤ 0.05) for cultures grown on MCA (25%–28%). When P. alliaceus was grown on standard CZA containing 0.3% NaNO3, only 5% of the stromata contained ascocarps. A greater percentage of the stromata (15%–22%) formed ascocarps when the NaNO3in CZA was replaced with an equivalent amount of available nitrogen supplied by ammonium tartrate, glutamic acid, or serine.Key words: ascospores, homothallic, sclerotia, essential amino acids.