Trichoderma gamsii, a new pathogen causing disease on cultivated mushroom Cordyceps militaris in China

The fungal disease of Cordyceps militaris has become the primary disease during the cultivation of C. militaris. However, some of the causal organism remains unclear. During our investigation in 2020–2022, three fungal strains were isolated from both the mycelium and fruiting bodies of C. militaris in mushroom farms located in Changchun. The observed disease incidence was approximately 20%. White villous mycelium on the surface of hyphae or fruiting bodies of C. militaris, is one of the main features of the disease, which can cause slow growth of mycelium, delayed primordia differentiation, and growth failure. Finally, the white cotton flocculent mycelium covered the surface of the medium, and the C. militaris stopped differentiating and failed to produce the primordium, ultimately leading to the stunted growth and lodging of the fruiting body. The objective of this study was to identify the pathogen based on Koch's Postulates, thereby confirming its pathogenicity and characterizing it through morphological and molecular features. The phylogenetic analyses showed that they belong to the Trichoderma gamsii. This study presented the first evidence of T. gamsii caused fungal disease in C. militaris, providing a theoretical basis for the prevention and control measures.