Characteristics of Characteristics of VirusVirusChapter 4 – AGR154

Overview of ChapterOverview of Chapter

Main characteristics of virusReproduction in virusVirus mode of attackTranslocation and distribution if viruses in plantDetection of virus or virus disease

Main CharacteristicsMain CharacteristicsVirus is a nucleoprotein (consist of nucleic acid and protein) and has the ability to cause diseaseThe protein will form a protective coat around the nucleic acid (capsid)The nucleic acid has either DNA or RNA but not bothThey may have two or more different proteinsParasitic in cellsMultiplies only in living cellsHas many shapes such as rod shaped, polyhedral.

Structure of VirusesStructure of Viruses

Polyhedral VirusHelical Virus

Reproduction in VirusReproduction in Virus

Virus do not divide and do not produce sporesDo not have specialized reproductive structuresMultiply by inducing host cell to make more virus

Virus Mode of AttackVirus Mode of AttackSo how do viruses cause injury?

By utilizing cellular substancesDuring multiplication, they take up space in cells and disrupting cellular processesViruses are small and transparentThey cannot be viewed and detected by methods used for other pathogensThey are not cells nor do they consist of cells

How They Injured Plant?How They Injured Plant?

They do not produce toxins They do not eat the host cellBut :

They utilize the host cellular substances for multiplicationConquer the host spaceDisrupt the host cellular process

How Do Virus Enter PlantsHow Do Virus Enter Plants

Through woundsBy vectorsInfected plant parts/ seedExample : Deposition of virus particle into ovule by infected pollen grain.

Translocation & Distribution Translocation & Distribution of Virus in Plantof Virus in Plant

1. Virus enter the host cell2. Moves from one cell to another cell

through plasmodesmata (connecting the cell)

3. Multiply in each host parenchyma cell4. Then, they will reach the phloem5. In phloem, the virus will be transported

rapidly over long distance.

7. From phloem, they will enter the host growing region (apical meristems and food utilizing parts)

Detection of Virus or Virus Detection of Virus or Virus DiseaseDisease

1. Inclusion BodiesSome infected plant will contain inclusion bodiesInclusion body : aggregation of virus particleThe inclusion bodies can be seen under a light microscope

Inclusion BodyInclusion Body

2. Virus ParticleThese can only be viewed under electron microscopeStill it is not easy to identify and difficult to prove that the particular virus cause the diseaseThe virus particle can be seen under electron microscope

3. Transmission Method

Transmit the virus from infected plant to healthy plant by:

Budding techniqueGraftingRubbing the leaves of healthy plant with the infected plant

4. SerologyMost common method is using the ELISA procedure

Enzyme-linked immunosorbent assay

5. DNA or RNA ProbesThis is the most recent methods