Since polyamines (PAS) play a potential role in the regulation of growth and developmental processes in a wide variety of organisms, we have examined the influence of the PAS putrescine (Put) and spermidine (Spd) and the PA biosynthetic inhibitors a-difluoromethylornithine (DFMO), adif luoromethylarginine (DFMA), methylglyoxal bis-(guanylhydrazone) (MGBG) and cyclohexylamine (CHA), singly and in combinations on microcycle conidiation (MC) in Aspergillus flaws. The exogenous application of the diamine Put (concentrations ranging from 01 to 5 mM) caused a sharp decline of MC in a dose-dependent fashion, but induced vegetative growth. However, the triamine Spd (01-5 mM) had a minimal effect on M C and induced a shift from M C to normal conidiation. PA inhibitors, especially DFMO, MGBG and CHA, produced greater inhibition of MC and complete inhibition of M C was observed at 5 mM of these inhibitors. DFMA even at 5 mM had only a weak inhibitory effect on MC. DFMO also inhibited conidial germination and germ tube growth. MGBG and CHA, while having an inhibitory effect on MC, induced vegetative growth. The inhibitory effect of PA inhibitors was partially reversed by exogenous Put or Spd, with Spd being more effective than Put. The analysis of free PA levels during various phases of M C revealed that undifferentiated spores contained a high Put/Spd ratio and there was a dramatic decrease in Put/Spd ratio before and during microcycle conidiophore maturity. The change in spermine titres could not be detected. These observations imply that Put is essential for vegetative growth, while S p d is involved in MC, and that a low Put/Spd ratio seems to be important for spore differentiation to MC.

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Microcycle conidiation in Trichoderma hamatum and T. harzianum has been achieved in complete darkness for the first time. The time required for mass conidiation without intervening vegetative growth was decreased to 24 h instead of 6 to 7 days. The conidia produced by microcycle conidiation were viable and had pigmentation and antagonistic behaviour similar to those of the parental stock cultures.

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