Melon necrotic spot virus facts for kids
Quick facts for kids Melon necrotic spot virus |
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| Melon necrotic spot on older leaf | |
Virus classification  |
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| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phylum: | Kitrinoviricota |
| Class: | Tolucaviricetes |
| Order: | Tolivirales |
| Family: | Tombusviridae |
| Genus: | Gammacarmovirus |
| Species: |
Melon necrotic spot virus
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The Melon necrotic spot virus (MNSV) is a virus that attacks plants. It belongs to a group of viruses called Gammacarmoviruses. This virus has been found in many countries across the Americas, Africa, Asia, and Europe. It is a common problem in greenhouses and fields where plants like melons, cucumbers, and watermelons are grown.
MNSV mainly spreads through infected soil, young plants (seedlings), insects, and a tiny fungus that lives in plant roots called Olpidium bornovanus. The signs of infection can be different for each plant. But generally, you might see leaves turning yellow, brown spots, wilting leaves, rotting fruit, and sometimes the whole plant dies. To stop the disease, farmers can rotate their crops, clean the soil with steam, and get rid of infected plants. Treating seeds with heat or special chemicals also helps prevent the virus from spreading. MNSV is a big problem for melon plants because it causes a lot of damage and reduces how many melons can be harvested. This leads to big money losses for farmers around the world.
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What Plants MNSV Attacks and How They Look
Melons are very important crops grown in warm and mild parts of the world. MNSV only attacks a small group of plants, mainly those in the cucumber and melon family. These include watermelons, cucumbers, and different types of melons like rockmelon and cantaloupe.
On watermelons, MNSV causes yellow spots on leaves, stems, or the first leaves that sprout (cotyledons). These spots then turn into dark brown areas. These brown spots mean that parts of the plant are dying. The fruit itself can also get infected. It might become strangely shaped, and the inside flesh can turn brown. In bad cases, the fruit might rot while still on the plant.
For cucumbers, MNSV causes yellow spots on leaves and cotyledons. Inside these yellow spots, tiny brown spots grow bigger, making the leaf or cotyledon wilt and die. The stems usually do not show these spots. The cucumber fruit itself does not get spots.
In melons, like rockmelon or cantaloupe, MNSV causes brown spots on the leaves and/or cotyledons. The roots also show brown spots. The melon fruit gets smaller and has brown spots on its skin.
Overall, when a plant gets MNSV, it will first show small yellow spots on its leaves, stems, or cotyledons. These spots then turn brown and get bigger. These dying spots can kill parts of the plant or even the whole plant. MNSV symptoms are usually worse when the weather is cooler. Once a plant is infected, the virus stays in it until the plant dies. If the virus is in the soil but no plants are infected, it can live in the soil for many years.
How MNSV Spreads (Life Cycle)
MNSV can spread in three main ways: through seeds, through the soil, and through living carriers (vectors). It spreads with the help of a soil fungus called Olpidium bornovanus, which needs moisture to move. It also spreads through certain cucumber beetles, like the western spotted cucumber beetle and the banded cucumber beetle. Since MNSV is a virus, it needs these vectors to move from one plant to another.
When seeds carry the virus, infection happens if these seeds are planted in soil that has the fungus but no virus yet. The virus from the seed is then released into the soil.
The virus sticks to the outside of the tiny swimming spores (called zoospores) of the Olpidium bornovanus fungus. It uses a special protein on its surface to attach. This fungus is only found in the roots of plants that are infected with the virus. Once the fungus enters the plant roots, it passes the virus to the host plant. This process then repeats when new seeds are formed.
Cucumber beetles also help spread MNSV. They prefer to eat the flowers of plants if they are available. This can reduce how much fruit the plant produces. If there are no flowers, the adult beetles will eat the leaves of melon and cucumber plants. This is how the beetles spread the virus in a lasting way.
Where MNSV is Found and What Conditions It Likes
MNSV can be found in warm and mild areas around the world where its host plants grow well. The first time MNSV symptoms were seen was in Japan. Since then, the virus has been reported to infect melons in Western Europe, Eastern Europe, the Americas, Asia, and Australia. In the United States, MNSV is mostly found in the southern states where the climate is good for it.
The symptoms of MNSV are usually seen during spring and autumn. This is because the virus needs high humidity and certain temperatures to cause problems. The virus starts to infect plants and show symptoms when temperatures are below 25°C (77°F). The most severe symptoms appear when temperatures drop slightly below 20°C (68°F).
How to Control MNSV
There are several ways to control MNSV. One way is to target the Olpidium bornovanus fungus, which helps spread the disease. Farmers can clean the soil using steam or certain chemicals to get rid of this fungus. Controlling pest insects, like the cucumber beetles, is also effective. Insecticides can kill these beetles, stopping them from spreading the virus.
Since MNSV lives in the soil, it is important to clean the soil and prevent the virus from spreading by machines. Removing and throwing away infected plants from the soil can help clean the soil. Also, cleaning farm machinery between different fields is very important. If infected soil stays on machines, it can spread the virus to other healthy fields. If too many plants in a field are infected, farmers might need to plant different crops there for a while (crop rotation).
The virus can also be carried by seeds. So, making sure seeds are clean before planting is very important. To get rid of MNSV in melon seeds without harming their ability to grow, they can be treated with heat for 144 hours at 70°C (158°F). Also, a chemical called Trisodium phosphate can be used effectively on infected seeds.
Finally, growing plants that are naturally resistant to the virus is the best way to control MNSV. Some melon types, like “Gulfstream” and a Korean type called PI 161375, are resistant. They have a special gene that helps them fight off MNSV.
Why MNSV is Important
Even though MNSV is not as well-known as some other plant diseases, it has caused major outbreaks. The virus was first discovered in 1966 in Japan by Kishi, who found it on melon plants in a greenhouse. For the next twenty years, there were smaller studies on how MNSV spreads.
In 1982, plant growers in Brough, England, first found the disease on their cucumber plants. By May 1983, some plants showed yellowing and occasional brown spots on their leaves. By August of that year, almost half of the 120,000 plants in the greenhouse were badly infected. By October, over 60% had MNSV. Luckily, the fruits of these plants did not show any symptoms, but the amount of cucumbers harvested was much lower.
For over forty years, this virus has been important because many people in farming did not know much about MNSV. Yet, it has the power to destroy a large part of a crop, as seen in the incident in England where over 60% of the crop was lost.
