Effect of nitrogen source on mycelial growth, blastospore production and thermotolerance of Cordyceps fumosorosea (Hypocreales: Cordycipitaceae)

Abstract

Among the entomogenous fungi, Cordyceps fumosorosea has great potential for the control of piercing-sucking insects in greenhouses. The blastospores of C. fumosorosea developed in liquid fermentation are more efficient for industrialization because they can kill insects faster and be produced faster than conidia from solid cultivation. Thermotolerance of blastospores plays a major role in their application in greenhouses. The added nutrient elements during its cultivation process have a significant impact on the thermotolerance of blastospores. Understanding the effects of nitrogen sources on the mycelial growth, sporulation and thermotolerance of C. fumosorosea is essential for its commercial application. Frequently used nitrogen sources were investigated in fermentation medium, including peptone, soya peptone, yeast extract, ammonium sulfate, urea and so on. Soya peptone provided the maximum blastospore yield and GT50, which were 5.17 × 108 blastospores mL−1 and 1.91 h, respectively. To explore the difference in intracellular substances involved in the thermotolerance of blastospores in the presence of different nitrogen sources, intracellular trehalose and mannitol were extracted and then qualified by ion chromatography. The results showed that blastospores with better thermotolerance generally had lower intracellular trehalose content, indicating that the intracellular trehalose content of blastospores could be a factor that the fungus responds to thermal stress and that its content in the blastospores could be adjusted by the supplemented nitrogen source.