immunofluorescence microscopy, immunogold labelling, and 

 conventional electron microscopy (leaf dips and ultrathin 

 sectioning). The preparation of ultrathin sections was 

 facilitated considerably by the development of a device for 

 simultaneous staining of 10 or more grids. 



Banded and crescent shaped inclusions were found in CyMV- 

 infected tissues stained with Azure A. Paracrystalline and 

 stacked-plate inclusions were formed in the ORSV-inf ected 

 tissues stained with either O/G combination or Azure A. In 

 CMV-infected tissues stained with Azure A, angular crystals 

 with or without clear centers were found. Cytoplasmic 

 cylindrical inclusions were observed in the BYMV-inf ected 

 tissues stained with the O/G combination. Nuclear inclusions 

 occurred in the bacilliform virus-infected tissues stained with 

 either the Azure A or O/G combination. 



Direct fluorescence microscopy confirmed the presence of 

 viral-related agents in the CyMV- , ORSV- and CMV-infected 

 tissues. Vanadyl molybdate-phosphotungstate (VaMo) negative 

 staining was used for confirming the presence of CyMV and ORSV. 

 Protein A-gold labelling was applied to identify CyMV, ORSV, 

 BYMV and CMV in the thin sections of tissues embedded in LR 

 White resin. 



Light microscopy was demonstrated to be a useful diagnostic 

 tool for orchid viruses. The diagnoses by light microscopy were 

 confirmed by VaMo negative staining, thin sectioning, 

 immunofluorescence microscopy and protein A-gold labelling. 



vii 



