Delayed Symptom Development Research Articles

A comparison of three low-persistence viruses of the strawberry

Three low-persistence viruses of mild, severe, and intermediate virulence, respectively, on strawberry (Fragaria vesca L.) seedlings have been isolated from Australian strawberry varieties. Studies concerned with the relationship of these viruses have shown that both the intermediate and severe types will multiply in F. vesea plants previously infected with the mild type of virus. Moreover, infection with this latter virus does not delay symptom development when the plants are inoculated with either the intermediate or severe types, and symptoms are intensified in each case. The mild and severe viruses were separated from mixed infections by serially transferring aphids (Pentatrichopus fragaefolii (Cock.)) bred on the infected plants. Separation was achieved by chance, and not as a result of different levels of persistence in the vector which the experiments were designed to exploit. In most instances both viruses were transmitted. The identity of the viruses is discussed in relation to known cross-protection phenomena.