Identification and Characterization of Three New Phalaenopsis Orchid-Infecting Viruses

A postulated so-called "Taiwan virus"-causing symptoms of chlorotic spots with centric necrosis or chlorotic ringspots on Phalaenopsis orchid leaves has been observed in Taiwan for several years. In 2002, a virus culture (91-orchid-1) was isolated from leaves of a Phalaenopsis orchid bearing chlorotic and necrotic spots from central Chinese Taipei. This virus was biologically, serologically and molecularly characterized. Results indicated that the virus is an isolate of Capsicum chlorosis virus (CaCV), designated as CaCV-Ph. In 2004, another virus-like symptom of chlorotic spots was observed on leaves of Phalaenopsis orchids in the central part of Chinese Taipei. A virus culture, Phalaenopsis isolate 7-2, was isolated from a symptomatic Phalaenopsis orchid. The causal agent was biologically and serologically characterized and shown to be a potyvirus that shares less than 70% amino acid identities with those of 18 other potyviruses that shared highest sequence identity in GenBank. Results from our study suggest that this is a new potyvirus and is designated as Phalaenopsis chlorotic spot virus (PhCSV). In 2003, a virus culture, 92-orchid-1, isolated from a Phalaenopsis orchid bearing chlorotic ring symptoms reacted with an antiserum to Carnation mottle virus (CarMV) in ELISA and its isometric particles measuring about 32 nm were observed. Sequence analyses of the CP gene showed that 92-orchid-1 is an isolate of CarMV and is therefore designated as CarMV-Ph. Specific antisera against CaCV-Ph, PhCSV and CarMV-Ph, and specific primers for RT-PCR were developed and successfully used for detection of these viruses. The occurrence of these three viruses in Phaelenopsis orchids has direct implication for the economically important nursery and floral industry in Chinese Taipei.