Recently, two different Mosaic viruses have been the cause of tomato crop decline in some Indian states. The problem has been persistent for the past few years. the mosaic family of viruses affects different species of plants. Read here to learn more about them and how plant diseases impact global food security.
Two separate viruses have been named by tomato farmers in Maharashtra and Karnataka for the loss of harvests earlier this year.
While growers in Karnataka and other South Indian states have attributed crop losses to the tomato mosaic virus (ToMV), farmers in Maharashtra have claimed that attacks of the cucumber mosaic virus (CMV) had an impact on their tomato crop.
Tomato growers have reported a rise in these two viruses’ invasion over the past three years, which has resulted in partial to complete crop losses.
Any virus that gives affected plant foliage a speckled look is referred to as a mosaic virus. Since these viruses originate from numerous distinct lineages, no taxon unifies all mosaic viruses.
- More than 150 different plant species, including several fruits, vegetables, and flowers, are affected by this virus.
- The leaves of this plant have dots or streaks of yellow, white, light and dark green, and other colors.
- The most frequently affected plants include cucumbers, tomatoes, potatoes, and squash.
Mosaic signs can be seen on both leaves and fruit and can vary in severity depending on the environment.
- The severity of the symptoms as the plant ages and grows depends on how young it was when it was infected.
- Infected plants that are still young may occasionally collapse and perish.
- At the flowering stage, infected plants may not produce fruit or their young fruits may fall off.
- Older or mature plants do not exhibit significant mosaics and can still yield edible fruit.
Plants cannot be treated with or protected by chemicals.
- Sanitation practices are the best way to manage and reduce infection. Get rid of all sick plants, including the roots, and any that are nearby.
- Mosaic viruses are incurable, like all viruses, yet occasionally they only produce attractively patterned leaves without seriously affecting a plant’s vigor.
Types of mosaic viruses
Many mosaic viruses commonly affect plants in the vegetable garden:
- Bean Common Mosaic Virus (BCMV) and Bean Yellow Mosaic Virus (BYMV) are the primary mosaic viruses that affect beans of all types. They are typically spread by aphids, but BCMV is also seed-borne, so do not save seeds from infected plants.
- Cucumber Mosaic Virus (CMV) is one of the most common mosaic viruses and tends to be spread by aphids. As can be inferred from its name, cucumber mosaic virus often affects cucumbers, but it is also a common problem for many other garden plants, including other cucurbits (melons, squashes), nightshades (tomatoes, peppers, eggplants, potatoes), and leafy greens (lettuce, spinach).
- Tobacco Mosaic Virus (TMV) spreads through seeds and direct contact, and the best way to avoid it is to grow resistant varieties.
CMV and ToMV, have similar names and cause equal 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 tomatoes, tobacco, peppers, and certain ornamental plants.
- Cucumber, melon, eggplant, tomato, carrot, lettuce, celery, cucurbits (members of the gourd family, including squash, pumpkin, zucchini, certain gourds, etc.), and other ornamentals are included in the considerably larger host pool of CMV. The virus was given its moniker, CMV after it was discovered in cucumber in 1934.
- Infected seeds, saplings, agricultural implements, and frequently the hands of nursery workers who failed to properly disinfect themselves before entering the fields are the main ways that ToMV spreads. A field might be completely overrun by the virus in a matter of days with just a few infected saplings.
- Aphids are sap-sucking insects that spread CMV. Although the likelihood of CMV spreading through human contact is exceedingly low, it is possible.
- High temperatures followed by brief periods of rain encourage the growth of aphids, which aid in the spread of CMV.
Control and Prevention
Once plants are infected, there is no cure for mosaic viruses. Hence, it is recommended to burn the infected material.
Prevention is key when it comes to viral infections in plants:
- Virus-resistant varieties are encouraged to be chosen for plantation.
- Mosaic viruses are mostly spread by insects, especially aphids and leafhoppers, hence control measures targeting them should be applied.
- Several weed varieties also serve as viral hosts, hence weed control is a necessity.
- It is important to follow biosafety standards in nurseries, and compulsory seed treatment to stop the spread of ToMV.
- 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 them to touch healthy ones.
Mosaic virus cannot be cured but the infection can be controlled with good agricultural practices.
Impact of plant diseases
Plant viral infections, which result in reduced yield and inferior-quality products, can result in significant economic losses.
- Developing nations, who are more likely to depend on agricultural production to maintain food security for the populace, may be particularly negatively impacted by this consequence.
- Additionally, to prevent the transmission of diseases across nations, severe sanitary rules may restrict the export of agricultural goods, which would exacerbate the effects of plant viral infections.
- Cropping patterns of the region may change and large-scale migrations may occur due to food insecurity.
Historically, numerous plant diseases have caused large-scale food security issues in countries.
- 1845-52 Irish potato famine caused by pathogen Phytophthora led to the death of an estimated one million people of hunger and the remaining had to take refuge in other parts of Europe for food and work.
- Other such examples include the Bengal famine (1942), the bacterial blight of rice in Bihar (1963), coffee rust in Sri Lanka (1867-1870), Downy mildew of grapes in France (1880s), and southern corn leaf blight in the USA (1970).
- However their excessive use has been a topic of debate over the years, and the fact that how the increased use of fertilizers may make plants more susceptible to diseases is also a point of contention.
A testament to the devastating effects of climate change that the world is currently experiencing is the large-scale floods, droughts, rising temperatures, and the accelerating melting of the polar ice. The flora is naturally impacted as well. In actuality, a surge in plant diseases has been connected to climate change.
International trade, and extreme weather events, all can act as carriers of plant disease outbreaks across borders.
- Hurricane Ivan in September 2004 aided soybean rust movement from Brazil to the United States.
Also read: Crop Residue Management
Hence, numerous factors need to be considered to control plant disease outbreaks.
- Experts agree that we must have effective surveillance systems that alert us to new infections.
- Rapidly developing “solutions to address the threats” is also crucial, but we don’t have a good framework for it now.
- Surveillance, improved detection systems, and global predictive disease modeling are important to mitigate disease outbreaks in plants and protect our global food supply.
Using genetically modified (GM) crops, which have been created to improve production by introducing plant disease resistance or increased herbicide tolerance, is one of the suggested ways to combat plant pandemics, and climate change, and eliminate world poverty.
Disease monitoring is especially crucial for a country like India where a majority of the working population is still linked to agriculture.
-Article by Swathi Satish