[Smart Farmers] Necrosis, deformity, slow growth, how to prevent and control plant viruses?

Plant viruses are a double-edged sword

The Netherlands is known as the kingdom of tulips. As early as the 16th century, many Dutch people spent a lot of money to buy tulips with colorful and messy patterns to decorate their gardens. This colorful splash-like flower is caused by infection with plant viruses.

In the 18th century, people began to use plant viruses to infect plants, causing petals to have spots or stripes on their original colors, thereby breeding varieties with more exotic and colorful colors. For example, tulips infected with tulip broken color virus will have white spots and stripes, while carnations infected with carnation mottle virus can produce five or six types of variegated flowers with different flower patterns.

Although people can use plant viruses to transform plants and cultivate flowers of various shapes, in most cases, plant viruses will seriously harm the yield and quality of crops, or even cause crop failure. Almost all crops will suffer from viral diseases, especially with global climate change, adjustments in agricultural industrial structure and cultivation patterns, and a surge in the area of ​​cash crops, viral diseases are becoming more and more common.

What are the common symptoms of plant viral diseases?

Common symptoms of viral diseases include mosaic, necrosis, and deformity.

1. Mosaic type

The typical symptoms of mosaic virus disease are irregular chlorosis, mottled patches of dark green and light green, or yellowing of leaves, with no obvious abnormalities in plant growth. In severe cases, in addition to the mottled patches, the veins of the diseased leaves are visible, and the plant grows slowly or becomes dwarfed.

2. Necrotic type

Some viral diseases can cause the death of local cells and tissues of plants, thus causing necrosis, which mainly manifests itself in branches, leaves, fruits and rhizomes. The necrosis of plants caused by viral diseases is different from that caused by bacterial diseases. The necrotic tissue caused by plant viruses does not have a foul odor.

3. Deformity <br /> Some viruses can cause various types of deformities such as curled leaves, shrunken leaves, wrinkled leaves, atrophy, clumps, dwarfing, and top shrinkage after infecting the host. This type of virus disease is mostly a chronic disease of the whole plant, often first occurring in young and tender parts such as the top heart leaves, showing symptoms such as mosaic, twisting, and shrinkage, and then spreading to other parts. Some virus diseases can cause local cell and tissue death in plants, causing necrosis, which is mainly manifested in branches, leaves, fruits, and rhizomes. Plant necrosis caused by viral diseases is different from necrosis caused by bacterial diseases. Necrotic tissue caused by plant viruses does not have a foul smell.

How do plant viruses spread?

Mechanical friction and insect-mediated transmission are the two main ways for plant viruses to spread. Seeds, pollen, and grafting can also spread plant viruses. Understanding the transmission methods of plant viruses is crucial for the prevention and control of viral diseases.

1. Mechanical transmission. Also known as sap friction transmission, it is mainly caused by contact between plants, agricultural operations, contamination of agricultural machinery and tools, human and animal activities, etc. Mechanical transmission is the main mode of transmission of some viruses (such as tobacco mosaic virus).

2. Transmission by insect vectors. Piercing-sucking insects and migratory pests such as aphids, planthoppers, and thrips are the main vectors of insect-borne viruses. These pests often spread a variety of viruses through piercing-sucking and feeding.

3. Seed transmission. Virus-carrying seeds can often cause early infection of the host and long-distance transmission of the virus. The hosts of seed-transmitted viruses are mostly plants of the Leguminosae, Cucurbitaceae, and Asteraceae, but very few of them are plants of the Solanaceae.

4. Pollen transmission. Currently, there are only a dozen viruses known to be directly transmitted by pollen, and most of them are woody hosts, such as peach ringspot virus and cherry leaf curl virus that harm cherries.

5. Spread through asexual propagation materials. Asexually propagated plants such as potatoes, garlic, and tulips are prone to virus transmission if the propagation materials are not completely sterilized. If the mother plant is infected, all offspring will be infected.

6. Grafting: Grafting is one of the commonly used agronomic measures for horticultural crops. Grafting can spread any kind of virus and virus-like diseases.

How to prevent and control plant viruses?

There are several main methods for preventing and controlling plant viruses:

1. Choose disease-resistant varieties. Breeding resistant varieties is the main means of preventing and controlling plant viruses.

2. Agricultural prevention and control. This includes strengthening seedbed management and cultivating disease-free and strong seedlings; implementing 2-3 year crop rotation, and rotating or intercropping with plants of different families as much as possible. Pay attention to field hygiene, and use soapy water to disinfect hands and tools in time during agricultural operations; agricultural operations should first treat healthy plants and then diseased plants to prevent human transmission. Diseased plants should be removed during transplanting, and if found, they should be removed in time, buried deep or burned to avoid the spread of the virus. Scientific fertilizer and water management promotes plant health and protects the susceptible stage.

3. Pest control. Timely control pests such as aphids and whiteflies that can spread viruses, cut off the transmission route, reduce the probability of viral diseases, and prevent their spread. For example, you can use yellow boards and black light to lure aphids, or use natural enemies to control insects, such as artificially releasing ladybugs, lacewings, aphid flies, and parasitic wasps to control aphids.

4. Chemical control. Pesticides cannot kill viruses directly, but insecticides such as imidacloprid, acetamiprid, and clothianidin can kill aphids, thrips, whiteflies, and other virus-transmitting insects, thereby effectively preventing and controlling viral diseases caused by cucumber mosaic virus and other diseases; or applying drugs such as guanidine hydrochloride and guanidine copper acetate that have a passivating effect on viruses, thereby inhibiting or delaying the occurrence of viral diseases, or applying drugs such as amino oligosaccharides and lentinan that enhance the immunity of crops to prevent virus infection or reduce virus damage.

Author: Yan Dankan, assistant researcher at the Institute of Plant Protection and Agricultural Product Quality and Safety, Anhui Academy of Agricultural Sciences.

Reviewer: Qi Rende, Researcher, Institute of Plant Protection and Agricultural Product Quality and Safety, Anhui Academy of Agricultural Sciences

Editor: Xie Yun