Importance of plants
Plants play important roles in purifying the air, providing a source of raw materials (wood), having medicinal values, providing a source of food, plays a part in nitrogen fixation and the list goes on. Since plants have such a crucial role in our lifestyle and maintaining the earth’s atmosphere and ecosystem it is important that plant diseases including those caused by viruses are studied.
Flow of Energy form sun to plant (autotrophs) and animals, etc (heterotrophs)
Nitrogen Fixation
Features of Plant Viruses
Plant viruses have a segmented genome divided into two or more nucleic acids which are enclosed within the virus particle. This unique characteristic can be used to distinguish plant viruses.
Plant viruses also have the ability to infect other multiple plant hosts causing different symptoms for different hosts. It is also from these disease symptoms from which viruses are named.
Structure of Plant Viruses
There are different types of structural morphology plant viruses can have which can be categorized according the viruses’ genomes. They are:
Transmission
The outer layer of plants tissues are composed of thick layers of waxes and pectin which protect the plant and have a thick cellulose cell wall. As a result viruses cannot readily penetrate into the plant’s cells and can only be introduced into the plant by breaching the cell wall.
The table below lists the various methods of transmission of plant viruses.
Means of Transmission
Living organisms can serve as vectors for transmission of viruses from one plant to another:
Control
There is no chemical method available for plants so the only way to prevent viral infection is to do the following:
· Remove plants which are infected and show symptoms
· Control the vector factor of transmission (e.g. control population of these vectors)
· Improve methods of plant cultivation.
Bacterial Viruses
The most common type of virus that infects bacteria are bacteriophages and hence they will be discussed in this section. Phage means ‘to eat’ so the name bacteriophage means to eat bacteria.
Features of Bacteriophages
The structure of the bacteriophage is a complex one which contains:
The bacteria phage’s genome also consists of modified bases which helps protect it from degradation from nucleases that break down host’s nucleic acids.
Fungal Viruses / Mycoviruses
There are a large variety of fungal viruses with over 60 species in 50 genera. However even though there is a large variety, very few viruses are studied in detail and most studies are done mostly with electron microscopes.
The first mycovirus discovered was found in a cultivated portobello mushroom in the 1950’s. The mushroom exhibited symptoms such as deterioration in tissue, change in morphology and decreased mushroom production.
Almost all fungal viruses have similar structural characteristics with a polyhedral structure and a double stranded DNA genome often with more than one dsDNA present per virus particle.
Viruses in Protista
There is very little information known about virus that infects the members in the kingdom of protista is limited.
