The effects of culture parameters on the conidial germination and yields of Ophiocordyceps sinensis

Abstract

Ophiocordyceps sinensis is an insect-born fungus with various biological and pharmacological activities. Artificial cultivation of the fungus-insect complex with fruiting body is not successful for the market mainly due to the lack of optimal conditions for fungus-insect interaction. Mass production of the pathogenic conidia as fungal inocula for effective insect infection is one of the critical steps. In this paper, the effects of different culture parameters on the conidial germination (defined in this study as the fungal colonies developed from the conidia on agar plates) and yields of two O. sinensis isolates were investigated on solid media. The conidia of two fungal isolates were unable to grow at 4°C or over 25°C. The better conidial germination was recorded on a solid medium (Medium C) containing 2.5% malt extract, 1.0% soluble starch and 0.9% agar at pH 6.0 at 14°C. Medium C was also optimal for harvesting conidial yield. Soluble starch stimulated conidial germination and yields. More nitrogen sources appeared to inhibit the germination and yields of the conidia. Fe3+ addition to the medium facilitated the conidial germination but hindered the conidial yields. These results provide a basis for optimal mass production of the conidia for insect infection and artificial production of the fungus-insect complex with fruiting body. Key words: Ophiocordyceps sinensis, conidia, conidial germination, culture parameter.