Longan witches broom-associated virus facts for kids
Quick facts for kids Longan witches broom-associated virus |
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Virus classification  |
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| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phylum: | Pisuviricota |
| Class: | Stelpaviricetes |
| Order: | Patatavirales |
| Family: | Potyviridae |
| Genus: | incertae sedis |
| Species: |
Longan witches broom-associated virus
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| Nations and subnational regions in China within which Longan witches broom-associated virus occurs (red) | |
| NCBI genome ID | KY649478 |
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| Genome size | 9428 nucleotides |
| Year of completion | 2017 |
The Longan Witches' Broom-Associated Virus (or LWBaV) is a tiny germ called a virus. It's a type of RNA virus, which means its genetic material is RNA. This virus belongs to a family called Potyviridae. Scientists believe it causes a plant disease called 'witch's broom' in longan trees. Longan trees (Dimocarpus longan) are important fruit trees grown in Southeast Asia. This disease was first noticed in 1941. The virus is found in sick longan plants, but not in healthy ones.
Contents
About the Virus's Name
The official name for this virus is Longan witches broom-associated virus. It's always written in italics, starts with a capital letter, and doesn't have an apostrophe.
There's also a specific type of this virus called 'longan witches' broom-associated virus'. This name isn't italicized or capitalized, but it does include an apostrophe.
In Chinese, the disease is called 龙眼鬼帚病毒 (Lóngyǎn guǐzhǒu bìngdú). In Vietnamese, it has several names, like chổi rồng trên nhãn and bệnh chùn ngọn.
Virus Family Tree
The Longan Witches' Broom-Associated Virus isn't very similar to other viruses in the Potyviridae family. It's most like viruses in the Tritimovirus group. However, scientists don't have enough proof to put it into that group. So, its exact place in the virus family tree is still 'incertae sedis', which means 'uncertain'.
Instead of comparing the virus's genetic code directly, scientists look at the proteins it makes. When they do this, they find its closest relative is the Rose yellow mosaic virus (RoYMV). More studies are needed to fully understand how these two viruses are related.
Virus Structure
The virus particles, called virions, are long and thin, like tiny threads. They are about 730 nanometers long and 14–16 nanometers wide. Inside each virus particle is a long strand of RNA. This RNA is about 9,428 nucleotides long. It contains the instructions for the virus to make its proteins.
How the Disease Spreads
Transmission Methods
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People first thought this disease was caused by a virus back in 1955. This was because it could spread through Grafting (joining parts of plants) and seeds. In 1972, a virus was found in sick leaves. However, this finding was debated because the results couldn't be easily repeated. This made scientists wonder if other things, like tiny bacteria called phytoplasma, or certain insects, were the cause.
Later, tests showed that treating plants with antibiotics didn't stop the disease. This meant phytoplasma were likely not the cause. Also, certain twig-boring insects were ruled out. The disease could appear on branches that weren't damaged by these insects. In 1990, a thread-like virus was found again, similar to the one from 1972.
The disease is spread by insects like the litchi stink bug (Tessaratoma papillosa) and the longan psylla (Cornegenapsylla sinica). The virus has been found in the spit glands of these insects. Because insects spread it, the virus might be related to one that affects lychee fruit. It could even spread to lychee plants through grafting. Other things that spread the virus include the longan gall mite and a parasitic plant called dodder. Infected pollen can also spread the virus, but plant sap cannot.
Unlike some other viruses, LWBaV doesn't seem to be spread by aphids. This is because its genetic code doesn't have the usual parts needed for aphid spread. Another insect, the planthopper Pyrops candelaria, also doesn't seem to spread the disease.
Resistant and Susceptible Plants
Some types of longan trees are more likely to get sick. These include 'Youtanben', 'Dongbi', and 'Honghezhi'. However, some longan varieties are very good at resisting the disease. These include 'Shuinan no. 1' and 'Lidongben'. The 'Fa Hok' variety can get sick, but it's tougher than some others.
One good way to fight the disease is to use healthy plant parts for grafting. It's also important to remove sick parts of plants. Controlling the insects that spread the virus is key. Using special sprays called miticides can greatly reduce the spread of the disease.
Where the Disease is Found
The Longan Witches' Broom disease is found in several countries. These include Vietnam, Taiwan, China, and Cambodia. In China, it's found in areas like Hainan and Guangdong. It was the first longan disease reported in Hong Kong. It likely arrived there from plants brought from Guangdong.
In affected longan groves, anywhere from 20% to 100% of the trees can be sick. Older groves often have a higher percentage of infected trees.
Symptoms of the Disease
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When a longan tree gets this disease, its young leaves don't grow properly. They might look twisted or have yellowed veins. New leaves are smaller, duller, and their edges curl up. Sick leaves often fall off early.
A key sign of the disease is when branches grow into thick, tangled clusters. These clusters look like a 'witch's broom', which gives the disease its name. The tree's flowers also don't grow normally. They become distorted and crowded. If fruit does grow, it's usually small and empty. Often, the flowers just fall off early, leaving behind a broom-like shape. Younger trees usually show more symptoms than older ones.
The virus itself is found inside the plant's food-carrying tubes, called sieve tubes. It usually sticks to the cell walls and membranes. The virus particles often clump together instead of being found alone.
It's important to note that damage from certain twig-boring insects can look similar to the symptoms of Longan Witches' Broom disease.
Images for kids
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Nations and subnational regions in China within which Longan witches broom-associated virus occurs (red)
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A litchi stink bug (Tessaratoma papillosa), one of the insects that can spread the disease.
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Healthy longan foliage
