MSc Huynh Kim Ngoc

What are viruses?

Viruses are biological units with very small size, no cell structure, average diameter from 20 to 300 nm (1 nm = 1/1,000,000 mm), which can only be seen through a electron microscope. Viruses can cause disease in humans, animals and plants. Viruses cannot live or grow in artificial environments, but must parasitize in the cells of humans or animals and plants that are suitable for them.

Structure of the virus:

Viruses have a very simple structure: The inner core is a nuclear acid (DNA, RNA), is by a shell composed of lipids, on which small protein particles are attached, so the virus is susceptible to infection. destroyed if exposed to alcohol (alcohol), alkali (savone) or high temperature.

Harmful way:

Viruses are obligate intracellular parasites because they can only live and multiply in the host is living cells.

This process proceeds as follows: Once entering the host cell, the virus that causes the disease will multiply rapidly by taking the nuclear acids, lipids, and proteins of the host cell to make its own cellular material. Host plants have metabolic disorders and show disease symptoms to the outside.

Viral diseases of plants:

Viruses cause damage to many crops such as diseases of  dwarf yellow rice, leaf curl dwarf , weedy rice (transmitted by planthoppers), cassava leaves mosaic disease (pathogen: whitefly), Greening on citrus (pathogens are Diaphorina citri), mosaic diseases on gourds, squash, melons, chili peppers, tobacco, papaya, sugarcane white leaf disease, Legionnaire is disease damages longan (Mycoplasma) etc.. The causative agent of the mosaic disease  are insects that belong to the group of suckers such as aphids, thrips, whiteflies, spiders, etc.

Spread and transmission of diseases:

Viruses cannot spread  to a large area by themselves. In humans, the virus is spread by surface contact, by inhalation, by needles, by blood transfusion, etc. In plants, the virus is transmitted by many routes: (1) through vectors. , mainly through sucking insects, (2) through cutting tools, pruning or mechanical wounds between diseased leaves and roots and healthy plants, (3) through asexual propagation such as cuttings, tubers, branches, roots, ... (4) through a few seeds of vegetables, tomatoes, beetroots, (5) through the soil (potato mosaic), (6) through fungi, nematodes, etc. However, the disease does not spread through water , air

Symptom:

The symptoms of viral diseases on plants are very diverse, depending on the cultivar, the time of infection, the cultivation conditions, the soil, the weather, the health status of the plants, etc. which symtoms manifest, severe or mild levels, affect productivity differently . In general, the sooner the disease is infected, the higher the yield is affected, the land is poor, the nutrient supply is poor, the trees are depleted, etc., the greater the loss .Symptoms of viral diseases on plants are very specific and easy to identify: If infected early, plants will be dwarf, stunted, stem grows lateral shoots, small leaves, shrunken veins, twisted, curved edges, torn, leaves turning green dark or light yellow, or alternating yellow-green, the leaf blade is not flat, rough, lumpy (mosaic). Rice with virus disease, plants with few grains, unfilled grains, cassava gets mosaic diseased with few tubers, fruits on diseased plants are small, deformed, poor quality, high fiber, less water.

Treatment:

On crops, there is no cure for viral diseases, only indirect prevention and control by means of killing vectors, which are sucking insects such as  hoppers , aphids, whiteflies, aphids, etc., with specific chemical products such as Osago 80WG, Sago super 20EC, Sec Saigon 25EC, SK Enspray 99EC mineral oil, etc. However, the most economical and effective measure is to use disease-free seeds, without taking tubers, cuttings, stems, and roots.. from infected plants to make seeds or grafts, pay attention not to plant thickly, plant in concentration, fertilize fully and balance, take care of healthy plants, in addition, it is necessary to visit the field regularly, especially in the period 1-2 months after planting, for early detection of diseased plants, uprooting and destruction, timely prevention and treatment with the above-mentioned special products, otherwise the disease will spread quickly and greatly affect the yield later.