Objective The objective of this study is to clarify the pathogenic fungi and its taxonomic status that cause stem rot in Anoectochilus roxburghii under facility cultivation and aseptic cultivation modes, and to screen out the fungicides with better control effect on the disease by combining fungicide bioassay.

Method The pathogenic fungi of A.roxburghii stem rot were obtained by tissue isolation, and the maximum likelihood method (ML) and Bayesian method were used for combined gene phylogenetic analysis, and the taxonomic status of pathogens was clarified by morphological identification. The mycelial growth rate method was used to screen out the fungicides with good effect on the pathogens of stem rot (ZJUP0240R and ZJUP1054-1).

Result The results showed that the A.roxburghii stem rot was caused by Fusarium oxysporum (Fo) in both facility cultivation and aseptic cultivation modes. The results of fungicides bioassays showed that four fungicides, including tebuconazole, difenoconazole, epoxiconazole, and pyraclostrobin, exhibited good inhibitory effects against the pathogens Fo ZJUP0240R and Fo ZJUP1054-1 of A.roxburghii stem rot. Among them, tebuconazole had an EC₅₀ value of 0.0652 mg/L and 0.0974 mg/L against Fo ZJUP0240R and Fo ZJUP1054-1, respectively; difenoconazole had an EC₅₀ value 0.0731 mg/L and 0.1222 mg/L against Fo ZJUP0240R and Fo ZJUP1054-1, respectively; epoxiconazole had an EC₅₀ value of 0.0166 mg/L and 0.0564 mg/L against Fo ZJUP0240R and Fo ZJUP1054-1 respectively; and pyraclostrobin had an EC₅₀ value of 2.5657 mg/L and 0.3696 mg/L against Fo ZJUP0240R and Fo ZJUP1054-1, respectively. The toxic effects of the pathogens of A.roxburghii stem rot (F. oxysporum ZJUP0240R and F. oxysporum ZJUP1054-1) to the four tested fungicides were as follows: epoxiconazole > tebuconazole > difenoconazole > pyraclostrobin.

Conclusion F. oxysporum is a pathogenic fungi of A.roxburghii stem rot under different cultivation modes, and the results of fungicide screening experiments show that triazole fungicides and strobilurins fungicides have a good effect on the mycelial inhibition of A.roxburghii stem rot pathogens, and the results of this study can provide a reference for the identification and chemical control of A.roxburghii stem rot.