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Cucumber mosaic virus (CMV) is a plant virus that attacks a number of species, including cucumbers and many other vining plants as well as tomatoes, potatoes and others. It is the most widely distributed plant virus in terms of possible affected species. CMV affects a large number of plants grown for food all over the world. It is known to be transmitted by aphids and sometimes seed. As with all plant viruses, there is no treatment for infected plants. The best defense against this virus is to grow resistant varieties and to eradicate infected crops to prevent spread.
Named for the crop group that it is most well known for attacking, the cucumber mosaic virus can do significant damage to cucumber and related vine crop species, like squash and melons. Under the warm and moist conditions favored by the numerous aphid species known to carry the virus, crop damage can be severe and even catastrophic with losses approaching 100%. It also attacks tomatoes, peppers, celery, and beans. Leaf crops like lettuces and spinach as well as many root crops such as potatoes and beets are also vulnerable. Many important fruit crops, such as bananas are also affected as well as many species of weeds and ornamental plants.
Symptoms of cucumber mosaic virus vary by species. In cucumbers, it affects all portions of the plant, including leaves and fruit. Leaves are mottled with spots and lines resembling a mosaic, hence the name, as well as often being abnormally wrinkled and curled. Cucumbers are often deformed and also mottled with whitish spots and a mosaic type pattern, and flavor is adversely affected, although the virus is not dangerous to humans. Infected plants exhibit very slow, reduced growth and flower production.
In other species, leaves often are reduced and have a wrinkled, curled, or narrowed growth pattern. The characteristic mosaic pattern of mottling with veins and spots is common. Overall growth is often stunted, and leaf shape in many plants is characterized by extreme narrowing. Leaf crops like lettuces often fail to develop good heads. The fruit, as well as all other parts of the plant, can be affected.
Since aphids are the primary transmission vector for this virus, its spread is often determined by the conditions which control aphid populations and spread, primarily weather. Warm and moist conditions favor the spread of aphids and, by extension, the cucumber mosaic virus. Very dry conditions seem to prevent its spread, and the virus is not found in arid regions. CMV is most active during warm periods but can survive in a dormant state in seeds and in dormant plant parts, such as roots, even through winter weather.
Control of the cucumber mosaic virus is primarily a matter of growing resistant varieties and destroying affected crops as soon as detected. Aphids, which spread the disease, spread rapidly when encountered, and can quickly infect large areas. Planting resistant varieties on the margins of fields and other varieties in the interior is one way of controlling the virus. A given aphid is only able to spread the disease for a very short time, and by the time it reaches the vulnerable varieties, it is no longer a carrier. Spraying mineral oil on plants to discourage aphids is another method of control.