Transmission of Plant Viruses

Last edited and updated on: January 13, 2020 by Sagar Aryal

Plant viruses are transmitted from plant to plant in several ways. The mode of transmission includes:

1. Vegetative propagation
2. Mechanically through sap
3. Through seed, pollen, dodder
4. By specific insects, mites, nematodes, and fungi

Image Sources: Crop Nutrition Laboratory Services Ltd. and https://doi.org/10.1111/1744-7917.12470

Transmission by Vegetative Propagation

• Whenever plants are propagated vegetatively by budding or grafting, any viruses present in the mother plant will almost always be transmitted to the progeny
• By cuttings, by bulbs, by corms, by rhizomes, by tubers, by runners or through natural root grafts of adjacent plants

Mechanical Transmission of Viruses through Sap

• In nature, the direct transfer of sap through contact of one plant with another is uncommon and relatively unimportant
• This method of transmission happens when the plants are wounded during cultural practices by tools, hands, or clothes, or by animals feeding on the plants
• In the mechanical transmission of viruses, a virus from one kind of plant may be transmitted to dozens of unrelated herbaceous plants
• However, several viruses, especially of woody plants, are difficult or impossible to transmit through the sap
• Examples of plant viruses transmitted through sap: potato virus X, tobacco mosaic virus and cucumber mosaic virus

Transmission of Viruses by Dodder

• Transmitted from one plant to another through the bridge formed between two plants by twining the stem of parasitic plants, dodder (Cuscuta sp.)
• Examples: sugar beet curly top virus (BCTV), cucumber mosaic virus

Seed Transmission

• More than 100 viruses are transmitted by seed
• The frequency of transmission varies with the host-virus combination and with the stage of growth of the mother plant when it is infected with the viruses
• The viruses seem to come primarily from the ovule of infected plants
• Examples: Barley stripe mosaic virus, Southern bean mosaic virus

Pollen Transmission

• Result in reduced fruit set, may infect the seed and the seedling
• In some cases, can spread through the fertilized flower and down into the mother plant
• Example: sour cherry with Prunus necrotic ringspot virus

Insect Transmission

• Most common and economically most important means of transmission
• Insect vectors of plant viruses:
  • Order Homoptera- Aphididae (aphids), Cicadellidae (leafhoppers), Delphacidae (planthopper), Aleyrodidae (whiteflies), Coccoidae (mealybugs), Membracidae (treehoppers)
  • Order Hemiptera- true bugs
  • Order Thysanoptera- chewing/sucking thrips
  • Order Coleoptera- beetles
  • Order Orthoptera- grasshoppers
• Insects with piercing and sucking mouthparts (stylet): aphids, leafhoppers, whiteflies, thrips, other groups of Homoptera, and true bugs
• Insects with chewing mouthparts: beetles and grasshoppers
• Examples: Grapevine virus A (transmitted by mealybugs and aphids), Turnip yellow mosaic virus (transmitted by beetles)

Mite Transmission

• Mites of family Eriophyidae is known as gall mites, family Tetranychidae
• These mites have piercing and sucking mouthparts
• Examples: wheat streak mosaic virus, peach mosaic virus, Ryegrass mosaic virus 

Nematode Transmission

• One or more species of three genera of soil-inhabiting, ectoparasitic nematodes
• Nematodes of genera Longidorus, Paralongidorus, and Xiphinema
  • transmit several polyhedral-shaped viruses (nepoviruses), such as grape fanleaf, tobacco ring spot
• Nematodes of genera Trichodorus and Paratrichodorus
  • transmit at least two rod-shaped tobraviruses, tobacco rattle, and pea early browning
• Transmit by feeding on roots of infected plants and moving on to roots of healthy plants

Fungus transmission

• Root-infecting fungal-like organisms, the plasmodiophoromycetes Polymyxa and Spongospora, and the chytridiomycete Olpidium transmit at least 30 plant viruses
• Transmitted by zoospores of root-infecting fungus and fungal-like organisms
• Examples of plant viruses vectored by zoospores:
  • Tobacco necrosis-type viruses
    • single-stranded RNA genome
    • Viruses are carried on the surface of zoospores, not internally
    • Acquired from the soil when the virus particles adhere to the surface of zoospore
  • Tobacco stunt type viruses
    • Rod-shaped viruses containing double-stranded RNA
    • Carried internally in the zoospores
    • They also enter the resting spores and survive in the soil
  • Barley yellow mosaic group viruses
    • Filamentous, single-stranded RNA viruses
    • These viruses acquired by the fungus within the plant cells and carried internally in both the zoospores and the resting spores
    • With very long persistence time in the soil
  • Furovirus group
    • Characteristically vectored by plasmodiophorid zoospores
    • Have a single-stranded RNA genome, which divided into two segments (RNA-1 and RNA-2) that occur in different virus particles
    • Acquired by fungus within the plant cells and carried internally in both the zoospores and resting spores
    • Example: Beet necrotic yellow vein virus

References

1. http://www.biologydiscussion.com/viruses/transmission-of-plant-viruses-8-methods-virology/64193
2. https://www.thoughtco.com/plant-viruses-373892
3. https://apsjournals.apsnet.org/doi/full/10.1094/PBIOMES-10-18-0045-R
4. https://www.thoughtco.com/plant-viruses-373892
5. https://www.annualreviews.org/doi/abs/10.1146/annurev.phyto.34.1.87
6. https://www.sciencedirect.com/science/article/pii/B9780444887283500160
7. https://www.ncbi.nlm.nih.gov/pubmed/15012536

Transmission of Plant Viruses