Why in CMV and ToMV virus news?
Tomato farmers in Maharashtra and Karnataka have attributed the decline in their yields earlier this year to two distinct viruses. Those in Maharashtra reported that their tomato crops were adversely affected by the cucumber mosaic virus (CMV), whereas growers in Karnataka and other South Indian states attributed their losses to the tomato mosaic virus (ToMV). In the past three years, farmers cultivating tomatoes have observed a rise in the prevalence of these two viruses, resulting in varying degrees of crop damage, ranging from partial to total loss.
What are CMV and ToMV?
The two plant pathogens, despite having similar names and causing similar crop damage, actually belong to different viral families and have distinct modes of transmission. The tomato mosaic virus (ToMV) is a member of the Virgaviridae family and shares a close relationship with the tobacco mosaic virus (TMV). It affects various plants, including tomatoes, tobacco, peppers, and certain ornamental plants.
- ToMV spreads through various means, including infected seeds, saplings, agricultural tools, and human contact.
- Certain insect vectors, such as thrips and whiteflies, can also transmit the virus.
- Infected plants display green mottling and yellowing of leaves, often appearing as blisters or fern-like patterns.
- Leaf curling in either an upward or downward direction and distortion may occur.
- Younger plants may experience stunted growth, and fruit setting can be affected.
Prevention and Control
- Emphasize the implementation of biosafety standards in nurseries and ensure compulsory seed treatment.
- Farmers should thoroughly inspect saplings before planting and discard any infected materials.
About cucumber mosaic virus (CMV)
On the other hand, the cucumber mosaic virus (CMV) has a much broader range of host plants. It can infect cucumber, melon, eggplant, tomato, carrot, lettuce, celery, cucurbits (such as squash, pumpkin, zucchini, and some gourds), as well as certain ornamental plants. The name “CMV” originated from its identification in cucumber back in 1934. It is worth noting that CMV has a wider host pool compared to ToMV.
- CMV primarily spreads through aphids, which are sap-sucking insects capable of acquiring and transmitting the virus within minutes.
- Transmission can also occur through infected seeds, mechanical inoculation, and grafting.
- Infected plants exhibit leaf distortion, primarily at the top and bottom, while the middle portion remains relatively unaffected.
- In cucumber plants, CMV causes a mosaic-like pattern of yellow and green spots on the leaves.
- Fruit formation can be adversely affected, resulting in stunting and reduced production.
Prevention and Control:
- The key focus should be on preventing aphids, the primary vector, by employing quick-acting insecticides or mineral oils.
- Care should be taken to avoid aphid migration and the spread of the virus to other fields.
Similarities between ToMV and CMV
Genome and Replication
- Both ToMV and CMV have a single-stranded RNA genome that is enclosed within a rod-shaped protein coat.
- Both viruses enter plant cells through wounds or natural openings and replicate within the cytoplasm.
- They can move systemically throughout the plant via the phloem, spreading to different parts of the plant.
Impact on Crop
- Both ToMV and CMV have the potential to cause significant crop losses, often approaching 100% if not adequately addressed in a timely manner.
- The severity of the crop loss depends on the susceptibility of the specific crop and the extent of infection.