Introduction to Plant Viruses

All Plant Viruses have these Common Properties

Some plant viruses have a very limited host range and others attack numerous species.

• Plant viruses can multiply only within living cells.
• Plant viruses usually multiply only within living plant cells, but some may be able to multiply within the bodies of aphids and nematodes.
• A given plant virus may be able to multiply only within the living cells of one species or genera of plants, but some can multiply within the cells of a wide group of plant families.
• I am not sure whether latent plant viruses exist. In general, most organisms harbor both virluent and and latent viruses.
• Plant viruses do not attack animals and vice versa.
• Temperate viruses embedd them selves within the hosts nucleic acid and are transmitted generation to generation just like genes of the host.
• Often viruses reside in their host without causing any disease or symptom. Such latent viruses are undiscovered.

Transmission of Plant Viruses

Plant viruses vary in their mode of transmission. Usually only a single mode of transmission is important, but some viruses are transmitted by more than one mode.

• Aphids or other sap-suckers are the most common mode of trannsmissiom
• Nematodes living in the soil transmitt some viruses.
• Sap transmission is important for only a few viruses and occurs on cultivators, pruning, hands of workers, and clothing of workers. Important for some potato viruses.
• Pollen transmission from male flower to female occurs for a few viruses. Such viruses are seed borne.
• Most viruses are do not get into the gametes and therefore are not seed-borne.

Detection of Plant Viruses

Until a virus is detected, its presence is not known. Nearly everyone who received an early polio vaccine is now a carrier of Simian Virus 40.(SV40). The monkey cells used to grow that vaccine were infected by SV40 but no one knew SV40 existed.

Many plants are carriers of plant viruses but show no disease. The yield might be reduced but that would not be visbible either.

The methods for detecting plant viruses include:

• Use of antibodies to the virus. In the ELISA assay, plant sap is placed in a plastic tray which contains wells and proteins, including virus, adsorb to the well. Then the the tray is washed under running water. then an antibody to the virus is added. A special enzyme has been bonded to the antibody. Very little of this antibody-enzyme binds to the well because all the plastic of the tray was covered with protein. Wash again. Now a colorless dye complex which the enzyme can split. The dye that is split free has color. The amount of color coorelates with the amount of virus present in the donor plant
• Graft a leaf from the suspected plant to an indicator plant. The virus moves into the host plant and causes symptoms in the indicator plant.
• Sap transmission. Place a drop of sap from the suspected plant on an intact leaf of an indicator plant. Add some grit to the sap and rub so the leaf is scratched and the virus, if any, can get into the leaf. If the indicator plant show symptoms then we know the virus came from the donor plant. The indicator plant for sweetpotato viruses is Brazilian Morning glory, tabacco, tomato, lambsquarter, and other plants are used as indicators in the sap and grafting assays.

Creating Virus-free Clones of Plants

It is not possible to cure a plant of viruses, but one of the following methods may give a virus free clone. Since the "virus-free" plant might contain a virus you did not know about, it is proper to call them virus-tested or virus indexed plants.

• Often the terminal bud of a plant is free of virus. Remove the 0.03 to 0.05 mm bud tip and grow it in sterile agar contain sucrose and everything the bud needs. 70 to 99.9% of the buds will rot or fail. If some grow to plants, test that plant bor virus as above and you might find one which is free of virus. Use it to start more plants. Be sure to test the plant for every known virus.
• Some viruses infect the tip also and the above method will not work. In such cases try growing the plant in an incubator that is so hot the plant barely grows. Often you must supply extra carbon dioxide at a very precise level. Then try to start a new plant as above and test it for all the known viruses.
• Most viruses are not seed-borne. Therefore, a new seedling may be free of virus. Test the seedling for all known viruses.

Once you have a virus-indexed plant keep it in a screened cage where it can't be infected via a vector. Alternatively, keep it on sugar agar in a sterile glass jar under fluorescent light at a low temperature where it grows slowly. Use scions from this microplant to grow plants for the field.

Precautions to keep your Plants Virus-free

• viricide your pruning tool between plants. use one volume of Chlorox plus nine volumes of clean water
• Keep the vectors away by screen, culture, or insecticides
• a few viruses can transmitted by clothing brushing against infected plants and then healthy plants. Never fear this transmission is very rare.

Additional Virus Problems

• Different strains of a given virus differ in symptoms and disease virulence just as different humans differ in their criminal activities and kindness.
• Your plant may have an unknown virus or a virus not expected for this plant.
• Some ornamental dwarf plants owe their short stature to a virus(es) and when cured they may grow too tall to be of interest.
• Such virus-dwarfed plants may spread virus to your healthy plants.
• Some plants having varigated foliage owe that beauty to a virus.

Other Indiana Biolab Pages about Plant Viruses

Indiana biolab has worked a few decades with plant viruses--especially since 1986. The pages below offer detailed information about viruses of specific plants.

• PK800 - Viruses of pumpkin, cucumbers, and related plants.
• ?????? - Viruses attacking sweetpotato
• ?????? - Viruses attacking strawberry
• ?????? - Viruses attacking cane berries (raspberry, blackberries)

Important Websites about Plant Viruses

http://image.fs.uidaho.edu/vide/descr267.htm - lists plant viruses.

http://image.fs.uidaho.edu/vide/famly050.htm - lists the species of plant which are susceptible to the virus you choose.

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you only have a few vines, you can consider pruning them on different days using a stainless steel knife, chlorox and soap. Remember your hands will carry the virus. You could wear rubber gloves and wash them in chlorox and soap. Drying will kill some viruses but not all.