ARS | Publication request: Culture Media and Sources of Nitrogen Promoting the Formation of Stromata and Ascocarps in Petromyces Alliaceus

Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract
Publication Acceptance Date: October 28, 2004
Publication Date: N/A

Technical Abstract: Petromyces alliaceus is the only known sexually reproducing fungus classified in Aspergillus section Flavi. The fungus was recently associated with ochratoxin A contamination that is occasionally observed in California fig orchards. When grown on solid culture media P. alliaceus produces numerous grey-black, sclerenchymatous stromata, some of which may slowly ripen to form ascocarps. Ascospores (meiospores) represent the principal source of genetic variation among naturally occurring clonal populations of P. alliaceus. 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 Petromyces alliaceus (NRRL 31813, 31814, 31816) isolated from crop field soils were grown on selected agar media in Petri dishes (7 mos. dark incubation, 30 deg C). 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 NaNO3 in CZA was replaced with an equivalent amount of available nitrogen supplied by ammonium tartrate, glutamic acid, or serine. The information should prove useful in supporting genetic investigations on the significance of recombinant diversity in ochratoxin A production, and in interpreting the contributions of fertile and non-fertile stromata in the fungal disease cycle which, like other species in Aspergillus section Flavi, may include insects as potential hosts.