Transmission of Plant Viruses

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

Transmission of Plant Viruses

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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



Transmission of Plant Viruses

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