Ca2+-dependent induction of conidiation in submerged cultures of Trichoderma viride

The presence of Ca2+ (up to 0.1 mol/L) in the cultivation media was found to induce the formation of conidia in submerged mycelia of Trichoderma viride in a concentration-dependent manner. Ca2+ dramatically stimulated conidiation after 70 h of cultivation. The effect was present in the dark, and illumination stimulated it only marginally. Low (less than 100 micromol/L) Ca2+ concentrations induced the formation of chlamydospores. Sr2+ could substitute Ca2+ in conidiogenesis with lower efficiency (almost 2 orders of magnitude), while the efficiency of Mg2+, Mn2+, or Ba2+ was lower by almost 3 orders of magnitude. Our results demonstrate that mycelial Ca2+ homeostasis has powerful effects on the conidiation and mycelial morphogenesis in T. viride, and they suggest that there is an additional mechanism of conidiation in addition to those induced by light and starvation.