The effects of growth media, temperature, pH and light on the
development of four isolates of Coniothyrium minitans (CONIO
and CH8 (colony type 3), G4 (colony type 4) and G9 (colony type 5))
were examined. Conidial germination, pycnidial production and hyphal
extension rate were initially studied on seven different agar-based
growth media at 18–20 °C. Potato-dextrose agar (PDA) and
malt extract agar (MEA) consistently gave the greatest conidial
germination, pycnidial production and hyphal extension rate for all
four isolates. Growth and development on molasses-yeast agar was
equivalent to that on PDA and MEA except that hyphal extension rate
was slower. Subsequently, the effects of temperature, pH and light on
the development of C. minitans were investigated on PDA
only. The temperature range of conidial germination and pycnidial
production of the four isolates was between 10–25° with the
optimum at approximately 20°. Hyphal extension occurred over a
greater temperature range, between 4 and 25°, with a maximum
extension rate of approximately 3·5 mm d−1
for all isolates occurring between 20–25°. Conidial
germination, pycnidial production and hyphal extension occurred over
a pH range between 3–8 with optimum values for all growth
assessments occurring between pH 4·5 and 5·6.
Increasing light period from continuous dark, to 12 h light/12 h
dark or continuous light had no effect on conidial germination or
extension growth, but significantly increased pycnidial
production.
Isolates G4 and G9, previously characterized by sparse production
of pycnidia in comparison with CONIO and CH8, consistently exhibited
a reduced production of pycnidia on all media, at all temperatures
and pH ranges, and all light regimes tested. This demonstrates the
stability of this character among these isolates of C.
minitans. The significance of these results for improving
production of inoculum of this biocontrol agent and in the
identification and classification of isolates of C. minitans
is discussed.