The transmission of beet mosaic and beet yellows viruses by aphides; a comparative study of a non-persistent and a persistent virus having host plants and vectors in common

The vectors of beet mosaic virus are optimally infective when they have fed for only a few minutes on the infected plants after a period of fasting. After infection feeding, infectivity is very rapidly lost when the vectors feed on healthy plants, but while it remains a single vector can infect several plants. Infectivity is lost much more slowly when the vectors fast after infection feeding. In this behaviour beet mosaic virus resembles Hy 3, potato Y, cucumber 1, and other aphis-transmitted viruses which have been called the non-persistent group. It resembles these viruses also in its physical properties. In some secondary characters beet mosaic differs from the other non-persistent viruses more than they differ from each other. It is retained longer by the fasting vectors, and infectivity of the vectors may increase considerably with increasing infection feeding time, in the absence of preliminary fasting, though it rarely reaches the optimal level. With beet yellows virus infectivity of the vectors is not affected by preliminary fasting, but always increases with increasing feeding time on both infected and healthy plants. Infectivity increases with increasing feeding time on the healthy plants whatever the infection feeding time, and therefore there is always a delay in the production of optimum infectivity by the aphides after cessation of infection feeding. Infectivity is more rapidly lost from the fasting than from the feeding vectors. The properties indicate that beet yellows belongs to the persistent group of viruses, although its persistence in the fasting vectors is only about the same as that of beet mosaic, which is a non-persistent virus. The main basis of distinction between the two types seems not to be the time for which they are retained by vectors, but the effect of preliminary fasting. Beet yellows and beet mosaic viruses have the same vector and host plant and therefore the differences in their behaviour are properties of the viruses them selves, and are not induced by the conditions in which they are transmitted.