CHAPTER 2 

 USE OF LIGHT MICROSCOPY TO DETECT AND DIAGNOSE 



ORCHID VIRUSES 



Introduction 



Odontoglossum ringspot ( ORSV ) and Cymbidium mosaic ( CyMV ) 

 are the best characterized orchid viruses, and several reliable 

 bioassay and electron microscopical and serological techniques 

 for their detection have already been developed (Appendix I, 

 Corbett, 1974; Inouye , 1977; Lawson and Ali, 1975; Lawson and 

 Brannigan, in press; Wisler e_t al. , 1982). Since the discovery 

 of these two viruses, at least 20 additional orchid viruses have 

 been reported, some of which induce debilitating diseases 

 (Lawson and Horst, 1984; Lawson and Brannigan, in press). However, 

 only 12 of these viruses are sufficiently characterized to be 

 assigned to groups by the International Committee for the 

 Taxonomy of Viruses (Matthews, 1982). This deficiency of 

 information can be attributed in part to a lack of convenient 

 diagnostic techniques, which is especially true for those 

 viruses that are not manually transmissible and for which 

 antisera have not been prepared. 



Light microscopy is useful for diagnosing viruses 

 representing 16 of the 28 recognized virus groups (Matthews, 



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