-2- 

 orchids , particularly CyMV and ORSV, is presumably due to three 

 factors: i) some are readily transmitted by contaminated 

 cutting tools used during propagation and flower harvesting; 

 ii) the genetic diversity of the Orchidaceae results in 

 variable symptom expression and therefore symptoms are 

 unreliable as a means of diagnosis ( Sheehan , 1980); and 

 iii) the viruses have been widely distributed through the 

 international exchange of individual plants. 



Bioassay and electron microscopical and serological 

 techniques have been used previously for detecting and 

 diagnosing some orchid viruses ( Lawson and Ali, 1975; Lawson 

 and Horst, 1984; Inouye, 1977; Lawson and Brannigan, in press; 

 Wisler et al . , 1982). For CyMV, ORSV, and certain other 

 orchid viruses, these methods have proven to be reliable and 

 practical. Certain bioassay and serological techniques have 

 been modified specifically for orchids (Appendix I; Wisler et 

 al . , 1982). However, such methods are not applicable for most 

 of the other orchid viruses listed by Lawson and Horst (1984). 

 This limitation is likely to be very significant to the orchid 

 industry, especially as some viruses have aerial vectors and 

 can spread rapidly in collections. Bioassays by manual 

 inoculation are not applicable to viruses such as the 

 Masdevallia isometric and Cypripedium filamentous viruses which 

 are apparently not transmissible by this means. Likewise, 

 serological techniques cannot be applied to any of the 

 rhabdoviruses for which antisera are not yet available. 



