Cucumber mosaic virus (CMV) is a plant disease-causing virus that has a worldwide distribution and a very broad host range. It was named so for one of the first plants in which it was found, the cucumber.
CMV is found predominantly in temperate areas around the world. CMV cannot live in extremely dry conditions. The optimal temperature at which CMV expresses itself and shows symptoms appears to be between 79 and 89 deg. F.
The CMV is very minute and is made up of ribonucleic acid core which is surrounded by a protein coat. They have no mode of self-dispersal; hence rely on various vectors to transmit them from infected to healthy plants. Once the virus infects a plant cell, the protein coat dissolves and the nucleic acid portion takes over the cell’s nucleic acid and protein synthesis systems and directs them to produce more viruses, thus disrupting and affecting normal activity in the cell. CMV cannot survive for long outside a cell or if the cell dies and can multiply only inside a living plant cell.
CMV may be spread from infected plants to healthy plants in the following ways:
- Several aphid species serve as vectors for CMV
- Mechanically by humans and tools through cultivating and even touching healthy plants after touching infected plants
- Through grafting
- Can also be transmitted by seed
Vegetables and fruits such as cucumbers and other cucurbits, squash, melons, bananas, artichokes, peppers, beans, peas, potato, tomatoes, carrots, celery, lettuce, spinach, beets, various weeds and many ornamental and bedding plants such as lily, delphinium, primula and daphne.
Damage and Symptoms
The following symptoms are may be associated with CMV:
- Mosaic yellowish patches or green and yellow mottling on leaves
- Stunted growth due to shortening of the internodes (length between stem and leaves)
- Downward curling of leaves that are distorted and small in size
- Distinct yellowing of the veins only
- Ring-spots or line patterns on leaves or fruits
- Reduced yields and distorted fruit and flowers
- White streaks on flowers known as “breaks”
CMV shows symptoms on leaves known as the “Shoestring” effect for most host species. This phenomenon causes young leaves to appear narrow and the entire plant to be stunted.
Specifically CMV can cause cucumbers to turn pale and bumpy. The leaves turn mosaic and their rugosity is changed, making leaves wrinkled and misshapen. Plant growth is stunted, few flowers are produced, and fruits are oddly shaped and appear gray. Cucumbers like this are often referred to as “white pickles”. Infected cucumbers are often bitter.
In celery, CMV can cause streaking and spotting. In lettuce, infected plants show symptoms of chlorosis, stunting and often do not properly form heads.
Pepper plants often have severe foliar damage, noticed as mosaic and necrotic rings. The peppers are often misshapen and contain chlorotic rings and spots.
Tomato plants when infected by CMV are usually stunted and have poorly shaped leaves, or “fernleaf”.
The CMV overwinters in perennial weeds, flowers and often crop plants. In spring when plants bloom and grow the virus emerges in the top leaves where it may be transmitted to healthy plants by aphid vectors (although tomatoes are not the preferred host of aphids) or by mechanical means. CMV cannot withstand very dry conditions nor can it persist in the soil. It also is more difficult than tobacco mosaic to transmit mechanically. Thus, cucumber mosaic tends to progress more slowly than tobacco mosaic in a field or garden.
Organic Means of Control and Prevention of Cucumber Mosaic Virus
There aren’t any known substances that cure a plant of CMV, nor any that can protect it from getting infected. Hence control measures for plant viruses include prevention and eradication.
– When purchasing seeds and plants, ensure that they are virus-free.
– Strictly maintain and prevent aphids from infesting your plants. Here’s an Aphid control guide.
– Remove all weeds as they are likely sources of both CMV and aphids. Groundsel and chickweed are particularly likely to harbor CMV.
– Immediately set aside suspect plants and obtain a diagnosis. CMV infected plants must be destroyed.
– Apart from aphids, CMV can be transmitted through gardening tools and by contact with infected plants. Maintaining clean and sanitized tools, machines and hands can go a long way in preventing the transmission of CMV.
– Use resistant varieties whenever possible. Zucchini- ‘Supremo’, ‘Defender’. Bush marrow- ‘Badger Cross’, ‘Zebra Cross F’, ‘Tiger Cross’. Cucumbers- ‘Bush Champion’, ‘Crispy Salad’, ‘Jazzer F’, ‘Paskia Fi’, ‘Petita’, ‘Country Fair’. Aubergine- ‘Bonica’. These varieties have shown some resistance to CMV.
– Trap crop method: In this method farmers plant resistant varieties around the perimeter of their fields and place susceptible plants in the middle. The intention of this that aphids will first land on the resistant varieties and by the time they have eaten their way to the susceptible varieties they will no longer be carrying the virus.
– Avoid your tomato plants from getting infected by CMV by not planting tomatoes next to cucurbits, spinach, or other vegetables and flowers susceptible to these diseases.