-68- 

 identical to those resulting from the mortar and pestle method, 

 described previously ( Lawson and Ali, 1975; Lawson and 

 Brannigan, in press). Discrete dark brown localized lesions are 

 typical of CyMV infections on Cassia cotyledons, whereas the 

 lesions induced by ORSV on Gomphrena leaves are light tan in 

 color. The lesion number in different tests will vary 

 according to the virus concentration in the orchid sample, the 

 condition of the indicator plants, and the skill of the 

 inoculator. Results can be recorded about one week after 

 inoculation if greenhouse temperatures are between 80-90 F. At 

 lower temperatures, slightly longer times may be required. 



Both the razor blade and the mortar and pestle techniques 

 are reasonably reliable methods of virus transmission. In a 

 comparative test involving 16 Cassia and 6 Gomphrena seedlings 

 inoculated by each method, an average of 12 lesions/ Cassia 

 cotyledon and 74 1 esions/ Gomphrena leaf were recorded when 

 razor blades were used in comparison to 5 lesions / Cassia 

 cotyledon and 43 1 esions/ Gomphrena leaf for the other method. 



The razor blade technique is recommended as a convenient 

 assay method for ORSV and CyMV, especially when large numbers 

 of orchid samples must be indexed. However, such 

 recommendations cannot be made for some of the other viruses 

 known to infect orchids. This is particularly true of those 

 viruses which may occur in low concentrations in their orchid 

 hosts or cannot be transmitted by rub-inoculation (e.g., the 

 Cypripedium filamentous and Masdevallia isometric viruses) 



