Leaves that had been infected during their development are usually deformed or involute. Frequently, lightened leaf areas, called chloroses , develop around the primary site of infection. Withered areas are called necroses . Chloroses are caused by a breakdown of the chlorophyll resulting in a decreased rate of photosynthesis. Heavy infections are characterized by a complete local loss of chlorophyll.
Affected areas have a yellowish look as only the carotenoids remain.
In nature, such strains are pretty rare since such a strong damaging of the host does also impair the virus chances of replication and spreading. Some viruses multiply within the plant without causing symptoms. This phenomenon is called latent infection . In contrast, wound tumor virus cause the development of tumors. The symptoms of most viruses are dependent on both virus and host, and do thus present an important diagnostic feature.