Pythium vexans Causing Stem Rot of Dendrobium in Yunnan Province, China

摘要

Since 2002 a severe root and stem disease of Dendrobiumhas occurred periodically each year in the plantationsof Simao City, Yunnan Province, China.Symptoms included water-soaked and brown lesions,and rot of tissues. Based on the morphological characteristicsand the internal transcribed spacer-1, 5.8Sribosomal RNA gene, and internal transcribed spacer2 and b-tubulin gene sequences, the pathogen wasidentified as Pythium vexans de Bary. The pathogenicityof the fungus was confirmed by satisfying Kochspostulates. This is the first world record of stem rot ofDendrobium caused by P. vexans.