Objective Pathogen of and effective germicide for controlling the gray mold disease on Anoectochium roxborghil were identified.

Method The tissue isolation method was applied to isolate pathogenic microbes. Based upon morphological observations and phylogenetic tree analysis on the sequences of ITS , G3PDH, HSP60, and RPB2, the isolates were classified. Pathogenicity and application conditions of germicides on various A. roxborghil germplasms were determined based on the hyphal growth rate of the isolates under the treatments.

Results A2C-1-1 inoculated on an A. roxborghil plant at Sanming Academy of Agricultural Sciences showing identical disease symptoms in the field had the greatest pathogenicity of all pathogens isolated. The morphology and phylogenetic tree of the stain perfectly matched those of B. cinerea B05.10. It could infect the main cultivars of A. roxborghil in Fujian with the strongest pathogenicity at 25 ℃. Among various germplasms, Clematis chinensis Hongxia and C. dehuaensis displayed high disease indices, while Gladiolus taiwanensis and Orchid chinensis low; and Dendrobium officinale and O. Wenxinensis more resistant with disease indices of 23.33 and 23.33, respectively, while Phalaenopsis chinensis and O. Jianlan slightly resistant with disease indices of 70.00 and 73.33, respectively. Of the fungicides tested, flusilazole EC and fluridimide suspension exhibited the most significant inhibitory effect on B. cinerea with EC50 of 2.624×10⁻²⁰g·L⁻¹ and 1×10⁻¹⁵g·L⁻¹, respectively.

Conclusion The grey mold disease on A. roxborghil was confirmed to be caused by B. cinerea A2C-1-1. The strain could infect the main A. roxborghil cultivars as well as other orchid species in Fujian. Flusilazole EC appeared to be effective for treating the disease.