The effect of different host plants of potato virus c in determining its transmission by aphids

A stock of potato virus C derived from Edgecote Purple potatoes in 1945 was not then transmitted by aphids, although more than 2000 aphids were used in conditions optimal for transmitting the serologically related potato virus Y. Thisstock of virus C has been propagated continuously since, by manual inoculation in a series of Nicotiana glutinosa and N. tabacum, and in 1955 it was transmitted by the aphid Myzus persicae (Sulz.): about one in twenty of the aphids transmitted it compared with one in two for potato virus Y. Virus C derived from the Edgecote Purple potatoes in 1955 was not transmitted by aphids; both stocks of virus C produced only local lesions in Majestic potato leaves, and gave similar symptoms in tobacco. When inoculated to Majestic potatoes and then returned to tobacco plants, potato virus C usually ceased to be aphid transmitted and did not recover this property in any of the subsequent subcultures. Transmission from stock by aphids did not isolate a strain of virus C which was any more readily transmitted by aphids, indeed, for the first two or three subcultures, aphids usually transmitted more readily from plants inoculated manually. But the few isolates which remained aphid transmissible, after a second passage through potato, were rather readily transmitted. These results suggest that the ability of a virus to be aphid transmitted is, at least in part, determined by the host plant in which it is multiplying, but the nature of the changes which determine this ability are unknown.