APPENDIX I 



A SIMPLIFIED BIOASSAY TECHNIQUE FOR 



CYMBIDIUM MOSAIC AND ODONTOGLOSSUM RINGSPOT VIRUSES 



Although there are a number of advanced techniques 

 available to detect orchid viruses, bioassay still remains a 

 popular, inexpensive, and reasonably reliable technique for 

 detecting Odontoglossum ringspot (ORSV) and Cymbidium mosaic 

 (CyMV) infections (Lawson and Ali, 1975; Lawson and Brannigan, 

 in press; Wisler and Zettler, in press; Zettler et al . , 1984). 

 Gomphrena globosa . is the laboratory indicator plant for ORSV 

 while Cassia occidentalis is used for CyMV. 



In the normal bioassay method, clean mortar and pestles 

 are used to extract juice from the orchid leaf sample, often in 

 the presence of a buffer solution (Lawson and Ali, 1975; Lawson 

 and Brannigan, in press). This juice is then rubbed onto the 

 leaves of indicator plants, which have previously been dusted 

 lightly with a fine abrasive (usually 300-600 mesh 

 Carborundum) . The abrasive produces microscopic wounds which 

 facilitate entry of the virus particles into the inoculated 

 leaves. To avoid carry-over of inoculum, the mortar and pestle 

 must be thoroughly cleaned (preferably sterilized) between 

 samples . 



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