Sheath and Root Rot of Phalaenopsis Caused by Fusarium solani

This study described that Fusarium solani (teleomorph Nectria haematococca) caused sheath and root rot of Phalaenopsis in Taiwan. In our field surveys since 2005, a fungal disease widely occurred in Phalaenopsis nurseries. The disease incidence of some susceptible varieties of Phalaenopsis was as high as 30 to 60% in certain nurseries. The diseased plants showed symptoms firstly on lower leaves which turned yellow with a sheath black rot period. The diseased leaves abscised after a short period of time, and eventually the infected orchid plants died. Usually, several small red granules (perithecia) with white mycelia were observed on the discolored sheath surface. In some cases, the disease lesions extended to the stems and roots which displayed brown to black rot with perithecia on the surface. Fusarium solani was isolated from 80% of the diseased tissues. Disease symptoms induced by an isolate FST1 of the suspected candidate pathogen of F. solani in greenhouse were identical to those observed in the field. Meanwhile, F. solani was recovered from the artificially inoculated diseased tissues. The perithecia of N. haematococca (sexual stage of F. solani) with salmon color were formed when single spores of FST1 were cultured on PDA at 24 degrees C for 2 to 3 weeks.