THE OCCURRENCE OF TOBACCO RATTLE AND TURNIP MOSAIC VIRUSES IN ORCHIS SSP., AND OF AN UNIDENTIFIED POTYVIRUS IN CYPRIPEDIUM CALCEOLUS

In extracts from Orchis militaris showing leaf mosaic and growth reduction filamentous particles with a normal length of 745 nm, and parts of pinwheel inclusions were detected. Following mechanical transmission the virus induced severe necrosis on inoculated leaves and systemic symptoms on Nicotiana clevelandii, and only local necrosis on Chenopodium quinoa. The virus reacted in IEM tests strongly with antiserum to turnip mosaic virus (TuMV), but only weakly with antisera to several other potyviruses. The serological reactivity, symptomatology, and cytopathology confirmed the similarity of the virus to TuMV. However, the virus could be differentiated serologically from typical isolates of TuMV using direct and indirect ELISA techniques. Differences from typical isolates of TuMV were also detected in the host range and in the extractability of the isolate, from plant tissues without addition of EDTA. The virus occurred also in other orchids of the same collection, infecting several species of the genera Aceras, Anacamptis, Barlia, Ophrys and Orchis.

In Cypripedium calceolus chlorotic and later necrotic streaks as well as leaf deformations occurred and were associated with a pinwheel-inducing filamentous virus measuring 774 nm, which as yet could not be experimentally transmitted. In IEM tests, the particles reacted more strongly with antiserum to TuMV than with antisera to several other potyviruses.

The occurrence of these partly widespread viruses in soil-inhabiting orchids may indicate a possible economic importance of these viruses also for epiphytic tropical orchids.

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