Cucumber Mosaic Virus (CMV) can cause severe losses in vegetables, legumes, and ornamentals. The virus is distributed worldwide, has a host range of more than 1,000 species, and is transmitted by at least 75 species of aphids. Host plants include both mono- and dicotyledonous plants, including many weed species.
Symptoms of CMV vary with viral strain, crop host and genotype, and environmental conditions. Symptoms can consist of necrotic specks, necrotic line patterns, or necrotic ringspots; stunting, chlorotic mosaics, narrowing of leaves and reduction in leaf size. Fruit symptoms include irregular ripening, wrinkled or bumpy appearance, a pale green coloration, and sunken, necotic lines or ringspots. The severity of CMV infection is closely related to plant age at the time of infection. Plants infected at a young age typically develop severe symptoms including mosaics, small, deformed leaves, and significant stunting. Mature plants tend to develop tolerance to CMV, remain symptomless, do not exhibit leaf deformation or stunting, and may have few fruit symptoms.
The broad host range of CMV and the large number of aphid vectors can result in its persistence. Some weed species including common milkweed (Asclepias syriaca), yellow rocket (Barbarea vulgaris), and yellow toadflax (or butter-and-eggs, Linaria vulgaris) can serve as resevoirs of CMV and contribute to spread of the virus early in the season and some (such as chickweed, Stellaria media) can serve as overwintering sites. Chickweed (and 19 other plants in the families Caryophyllaceae, Chenopodaceae, Amaranthacaeae, Fabaceae, Brassicaceae, and Lamiaceae) can also spread the virus through dissemination of infected seed.
Fruit size and the number of marketable fruit may be reduced.
Cultural Controls & Prevention:
- Resistant and tolerant pepper cultivars are available, but no resistant tomato varieties are available. There are also effective resistant varieties of cucumber available.
- Trans-gene-mediated resistance against CMV may be possible in other crops.
- Cultural practices that delay the introduction of CMV include elimination of weed hosts, timing planting to avoid aphid populations and migrations, and the use of reflective mulches to deter aphids.
- Insecticides are not recommended due to their general low level of effectiveness. CMV is transmitted nonpersistently by aphids and transmission occurs too rapidly for insecticides to be effective.
- Plant growth promoting bacteria that induce the plants' natural defenses has been successful in tomato.