Detection of the pathogenic fungus Cordyceps farinosa in the Thitarodes armoricanus soil-rearing environment based on nucleic acid targets.

Cordyceps farinosa, an entomopathogenic fungus, infects and leads to high mortality of Thitarodes armoricanus larvae, which die soon after the infection of C. farinose, usually before the colonization of Ophiocordyceps sinensis owing to competitive inhibition and fruiting body formation. Therefore, monitoring C. farinosa in the O. sinensis cultivation environment is critical for minimizing the C. farinosa infection-induced losses. In this study, we initially designed a PCR primer pair (Tar-1F/Tar-1R) through open reading frame prediction and homology comparison of the C. farinosa genome sequence. This primer pair can detect both C. farinosa and Samsoniella hepiali. To further distinguish, primers (ITS5-172/ITS4-95) were then designed to selectively amplify the large ribosomal subunit sequences in the C. farinosa genome. All these primers were applied in combination for detection of C. farinosa in soil samples. The sensitivity reached a detection limit of 1 × 10⁶ spores/g soil. In addition, these primers can detect the presence of C. farinosa in dead T. armoricanus larval samples. This newly established rapid detection method provides important information for C. farinosa control during O. sinensis cultivation.