Tomato growers in Maharashtra and Karnataka have been grappling with reduced yields due to the presence of different viruses. The cucumber mosaic virus (CMV) has affected crops in Maharashtra, while the tomato mosaic virus (ToMV) has impacted tomato crops in Karnataka and other South Indian states.
Understanding CMV and ToMV
While CMV and ToMV share similar names and inflict similar damage on crops, they belong to different viral families and spread differently. ToMV belongs to the Virgaviridae family and is closely related to the tobacco mosaic virus (TMV). It affects plants such as tomatoes, tobacco, peppers, and certain ornamental plants. On the other hand, CMV has a much larger host pool, including cucumber, melon, eggplant, tomato, carrot, lettuce, celery, cucurbits, and some ornamentals. CMV derived its name from its identification in cucumbers in 1934.
Spreading Mechanisms
ToMV primarily spreads through infected seeds, saplings, and agricultural tools. It can also be transmitted by nursery workers who have not adequately sanitized themselves before entering the fields. CMV, on the other hand, is mainly spread by aphids, sap-sucking insects. While CMV can be transmitted through human touch, the chances of this occurring are minimal. Conditions of high temperature followed by intermittent rain create a favorable environment for aphids to multiply, leading to the spread of CMV.
Impact on Crop
- ToMV-infected plants exhibit alternating yellowish and dark green areas on the foliage, often appearing as blisters on the leaves. Leaf distortion and twisting of younger leaves are common symptoms. The fruit may develop necrotic spots, leading to premature ripening. Younger plants may be stunted, and fruit setting can be affected.
- CMV also causes leaf distortion, but the pattern differs. Typically, the top and bottom leaves are distorted, while those in the middle remain relatively blemish-free. In cucumbers, the virus induces a mosaic-like pattern of alternating yellow and green spots. In tomatoes, fruit formation is affected, and in some cases, the fruit may be distorted and small.
Control Measures
- To mitigate the spread of these viruses, it is crucial to adhere to biosafety standards in nurseries and implement compulsory seed treatment to prevent the transmission of ToMV. Farmers purchasing trays of saplings should carefully inspect them before planting and discard any visibly infected material. Vigilance is essential throughout the cropping cycle, with infected plants promptly removed to prevent contact with healthy ones.
- Maintaining a clean field environment is essential. Weeds and plant material should be cleared before fresh planting. While infected plants cannot be cured of ToMV, the infection can be controlled by implementing good agricultural practices.
