The specificity of transmission of some non-persistent viruses

When leaves infected with potato virus Y and other non-persistent viruses were exposed to ultraviolet light the infectivity of their expressed saps was reduced to about one fifth of that of the controls, suggesting that the viruses were much more concentrated in the epidermis than elsewhere in the leaves. Non-persistent viruses are usually transmitted by aphids much more readily after about two minutes feeding on infected leaves than after longer times. With irradiated leaves there was no greater ability after short than after long infection feeding times. Brevicoryne brassicae (L) does not transmit cauliflower mosaic virus optimally after 2 minutes infection feeding, and its ability to transmit is not affected by irradiation of the infected leaf on which it feeds. Myzus persicase (Sulz) on the other hand transmits cauliflower mosaic in the same manner as other non-persistent viruses and irradiation reduces its ability to transmit after short infection feeds. Potato virus C is serlogically related to potato virus Y and both are similarly affected by ultraviolet irradiation. But potato virus Y is readily aphid-transmissible and potato virus C, according to previous workers, not at all. A culture of potato virus C maintained for 8 years in Nicotiana glutinosa became transmissible by Myzus persicae, though less readily than potato virus Y. When inoculated to majestic potato and returned to tobacco this culture usually again reverted to one not transmitted by aphids. The ability of a virus to be transmitted by aphid cannot be correlated with any known physical or chemical property; nor with its distribution in the leaf or susceptibility to secretions by aphids. Present evidence suggests that it perhaps depends on the virus particle having some special group, probably only a small part of its total constitution, that combines specifically with some component of the aphid's mouthparts.