Tomato Mosaic Tobamovirus, Causal Agent of a Severe Disease of Pepino (Solanum muricatum).

Abstract

Pepino (Solanum muricatum Aiton), a vegetatively propagated herbaceous crop from the Andes, is esteemed for its edible, juicy, and fragrant fruits. Its cultivation as a crop for diversification is increasing in many frost-free areas throughout the world (2). In 1994, a severe viruslike disease, previously undescribed, was observed on pepino plants in Valencia, Spain. The disease has continued to cause economic losses in pepino plantings in subsequent years. Symptoms, which are exacerbated at temperatures above 30°C, include dark and light green mosaic predominantly in young leaves, leaf puckering and distortion, short internodes, fruit deformation, delay in ripening, and yield reduction. Samples from affected plants were analyzed by enzyme-linked immunosorbent assay (ELISA). All samples displaying viruslike symptoms reacted positively with antiserum made against tomato mosaic tobamovirus (ToMV) but not with antisera made against alfalfa mosaic alfamovirus, cucumber mosaic cucumovirus, potato Y potyvirus, tobacco mosaic tobamovirus, tomato spotted wilt tospovirus, or tomato yellow leaf curl bigeminivirus. A leaf extract from diseased plants was heated at 72°C for 10 min. This treatment inactivates most plant viruses but does not eliminate infectivity of ToMV (1). Inoculation of a collection of pepino clones resulted in the development of symptoms in most clones. Symptomatic clones were also ELISA-positive for ToMV. A few clones showed a hypersensitive reaction, which consisted of the development of necrotic lesions in the inoculated area. New growth on these clones was asymptomatic and ELISA-negative for ToMV. These results clearly point to a causal relationship between ToMV infection and the observed disease. The initial source of the infection should be eliminated from commercial plantings, as ToMV is easily transmitted when the pepino plants are trellised and pruned. Special care must also be taken to ensure that mother plants from which cuttings are taken are free from this virus. In addition, ToMV is usually found in meristematic tissues, even after thermotherapy and chemotherapy treatments are applied, making the regeneration of virus-free plants from infected clones by meristem tip culture difficult. Therefore, it seems that the best strategy against this disease is the development of resistant cultivars.