CMV and ToMV Viruses

What’s in today’s article?

• Why in News?
• What are CMV and ToMV?
• How do these Two Viruses Spread?
• How do Viruses Affect the Crop?
• How can the Viruses be Controlled?

 

Why in News?

• Tomato growers in Maharashtra and Karnataka have blamed two different viruses for the loss of yields earlier this year.
• Farmers in Maharashtra have said their tomato crop was impacted by attacks of the cucumber mosaic virus (CMV), while growers in Karnataka and other South Indian states have blamed the tomato mosaic virus (ToMV) for crop losses.

 

What are CMV and ToMV?

• The two plant pathogens have similar names and cause similar damage to crops, but 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). ToMV hosts include tomato, tobacco, peppers, and certain ornamental plants.
• CMV has a much larger host pool that includes cucumber, melon, eggplant, tomato, carrot, lettuce, celery, cucurbits (members of the gourd family, including squash, pumpkin, zucchini, some gourds, etc.), and some ornamentals.
• Over the last three years, growers of tomato have complained of increased infestation with these two viruses, leading to partial to complete crop losses.

 

How do these Two Viruses Spread?

• ToMV spreads mainly through infected seeds, saplings, agricultural tools and often, through the hands of nursery workers who have failed to sanitise themselves properly before entering the fields.
  • It would require only a few infected saplings for the virus to take over an entire field in a matter of days.
  • For ToMV, farmers in Maharashtra have blamed seed manufacturers and nurseries.
• CMV is spread by aphids, which are sap-sucking insects. CMV too can spread through human touch, but the chances of that are extremely low.
  • Conditions of high temperature followed by intermittent rain, which allow aphids to multiply, are conducive to the spread of CMV.
  • These conditions were seen in Maharashtra - the late rabi crop (planted in January-February) faced a sudden bout of rain followed by extreme heat.

 

How do Viruses Affect the Crop?

• Both viruses can cause almost 100% crop loss unless properly treated on time.
• The foliage of plants infected with ToMV shows alternating yellowish and dark green areas, which often appear as blisters on the leaves.
  • Distortion of leaves and twisting of younger leaves are also symptoms.
  • The fruit develops necrotic spots, which leads to overripening.
  • Younger plants are dwarfed and fruit setting is affected.
• CMV too causes distortion of leaves, but the pattern is different. Often leaves at the top and bottom are distorted while those in the middle remain relatively blemish-free.
  • In cucumber, the virus causes a mosaic-like pattern of alternating yellow and green spots.
  • In tomato, fruit formation is affected and in some cases the fruit is distorted and small.
  • Overall, CMV causes stunting and lower production.

 

 

How can the Viruses be Controlled?

• Plants cannot be cured of ToMV, but the infection can be controlled with good agricultural practices.
  • It is very important to ensure that nurseries maintain biosafety and restrict entry into the premises.
  • Seed treatment at the nursery is necessary to prevent future spread of the virus.
  • Farmers who buy trays of saplings should check before planting and discard any visible infected material.
  • They should also look out for signs of infection throughout the cropping cycle and remove infected plants without allowing it to touch healthy ones.
  • Fields must be cleared of weeds and plant material (ToMV can remain dormant in weeds and plant remains) before fresh planting.
• Controlling CMV is more difficult, given the large number of hosts the virus can live on.
  • The best way is to stop the aphids, which can be done by spraying quick acting insecticides or mineral oils on the plants.
  • Irritating the aphids can spread the virus to other fields.
  • An eye must be kept on aphid migration so that measures can be taken while planting the crop.

 

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Q1) What is biosafety and why it is important?

According to the WHO, biosafety is a strategic and integrated approach to analysing and managing relevant risks to human, animal and plant life and health and associated risks for the environment.

 

Q2) Which is the most famous plant viral disease in India?

Yellow mosaic disease (YMD) caused by begomoviruses transmitted through the insect vector Bemisia tabaci poses a serious threat to the production of legume crops.

 

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Source: CMV and ToMV: The two ‘mosaic’ viruses that hit tomato crop in Maharashtra and Karnataka