Production, survival and efficacy of Coniothyrium minitans conidia produced in shaken liquid culture

Abstract

Coniothyrium minitans is a fungal biocontrol agent of the plant pathogen Sclerotinia sclerotiorum. Growth and sporulation of 21 strains of C. minitans were examined on potato dextrose agar (PDA) and compared with that in potato dextrose broth (PDB) in shaken culture after 12 days at 20 degrees C, to identify strains with potential for inoculum production in liquid culture. Four strains that produced high numbers of pycnidia in PDA also formed pycnidia on mycelial strands in PDB and 10(7) conidia ml(-1) broth were produced. The other strains formed pellets during shaking, resulting in production of less than 10(5) conidia ml(-1). Conidia from shaken PDB culture had the same ability to infect and rot sclerotia of S. sclerotiorum as conidia produced routinely on PDA, and survived well in dry kaolin dust for 6 months at temperatures less than 8 degrees C with less than 1 log(10) colony forming units mg(-1) loss. These results suggest that it might be possible to identify useful strains of C. minitans for future commercial conidial production in liquid fermentation systems based on morphological characteristics on agar.