Clonostachys rosea, a Pathogen of Brown Rot in Gastrodia elata in China

<i>Gastrodia elata</i>, commonly known as Tian Ma, is a perennial mycoheterotrophic orchid. Qianyang Tian Ma (QTM), a geographical indication agricultural product from Hongjiang City, Hunan Province, China, is primarily characterized by the red variety, <i>G. elata</i> f. <i>elata</i>. A severe outbreak of tuber brown rot disease was documented in QTM during the harvesting season in Hunan. The fungal pathogen associated with the disease was isolated on potato saccharose agar (PSA) and identified through morphological and phylogenetic analyses. Pathogenicity tests were performed on healthy tubers of <i>G. elata</i> f. <i>elata</i>. The results showed that the representative isolate, named TMB, produced white hyphal colonies with a ring structure, broom-like phialides, partially curved ellipsoidal conidia, and orange-yellow spherical ascocarps on PSA. Phylogenetic analysis of the ITS, LSU, <i>rpb2</i> and <i>tub2</i> sequences using Bayesian and maximum-likelihood methods identified the isolate TMB as <i>Clonostachys rosea</i>, based on morphological and phylogenetic data. Pathogenicity tests revealed typical disease symptoms on healthy <i>G. elata</i> tubers 15 days post-inoculation with the isolate TMB. <i>C. rosea</i> is known to cause diseases in economically important crops, but there are no reports of its occurrence on <i>G. elata</i> f. <i>elata</i> in China. This study provides valuable insights into the occurrence, prevention, and control of brown rot disease in <i>G. elata</i> f. <i>elata</i>.