Cucumber mosaic virus (CMV) is one of the most widespread and troublesome viruses infecting cultivated plants worldwide. The diseases caused by CMV present a variety of global management problems in a wide range of agricultural and ecological settings. The elevated magnitude of risk posed by CMV is due to its broad host range and high number of arthropod vectors. The pandemic distribution of cucumber mosaic, coupled with the fact that it typically causes 10-20% yield loss where it occurs (although it can cause 100% losses in cucurbits) makes it an agricultural disease of major importance.
Cucumber mosaic virus (CMV) is a plant pathogenic virus is the family Bromoviridae. It is the type member of the plant virus, genus, Cucumovirus. This virus has a worldwide distribution and a very wide host range. In fact, it has the reputation of having the widest host range of any known plant virus. Cucumber Mosaic disease transferred as virus from one infected plant to another through the bite of an aphid.
The infection is acquired by the aphid in just one minute after ingestion and is gone within hours. Great for the aphid, but unfortunate for the hundreds of plants it can bite during those few hours. Fortunately, Cucumber Mosaic Virus is not passed down from generation to generation as it cannot be passed along via seeds and does not survive very long in plant debris or soil.
The pathogen causing cucumber mosaic disease(s) is Cucumber mosaic cucumovirus, although it is also known by other names, including Cucumber virus 1, Cucumis virus 1, Marmor cucumeris, Spinach Blight Virus, and Tomato Fern Leaf Virus. This virus was first found in cucumbers (Cucumis sativus) showing mosaic symptoms in 1934, hence the name Cucumber mosaic.
Since it was first recognized, it has been found to infect a great variety of other plants. These include other vegetables such as squash, melons, peppers, beans, tomatoes, carrots, celery, lettuce, spinach, and beets. Various weeds and many ornamentals and bedding plants, such as Narcissus.
Cucumber Mosaic Virus symptoms are rarely seen in cucumber seedlings. Signs become visible at about six weeks during vigorous growth. The symptoms vary widely depending on the crop infected and the plants stage of development when the infection first occurs. They also vary with the species of plant infected and the environmental conditions. In some cases, certain environmental conditions bring out symptoms while other conditions mask or hide symptoms. Symptoms associated with CMV infections are yellowish patches or green and yellow mottling on leaves.
Symptoms of CMV in lettuce can be similar to those of lettuce mosaic virus. Infected plants show symptoms of chlorosis, stunting and often do not properly head. CMV in peppers causes slightly different symptoms than the previously mentioned. Pepper plants often have severe foliar damage, shown as mosaic and necrotic rings. Often the peppers themselves are misshapen and contain chlorotic rings and spots.
Cucumber beetles and more than 60 species of aphids vector and transmit CMV.
The disease is readily transmitted between plants via plant sap and by mechanical inoculation via pruning tools. Transmission to new plants through seeds occurs to varying degrees for 19 host species, including some important weeds.
The geographic dispersal by and the durable persistence of CMV in weed seeds are important factors in the dynamics and epidemiology of some diseases caused by CMV. This virus can also be transmitted between plants by parasitic seed plants such as dodder (Cuscuta spp.), whose vine-like stems bridge the hosts aerially or at the ground surface.
No chemicals can cure a plant of this virus infection or of any other. It is recommended that if Cucumber Mosaic Virus affects your cucumber plants, they should be removed immediately from the field to reduce the risk of transmission. Avoid handling healthy plants after working with suspected infected ones until tools or hands have been washed with soapy water and choose resistant cultivars.
Bolton Kudzai Kakava is a Plant Pathologist/Agronomist/Food and Agriculture Standards Consultant
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