Importance of Plant protection and plant viruses
Food, Clothing, feed stuffs, housing, furniture etc., and many recreational activities depend on plant production. Plant pathogens are a huge threat to plant production. Damage is brought about by pests, diseases, weeds, storage, production of secondary metabolites, environmental factors and human practices. About 30–40% loss is brought about due to damage by pathogens that contribute to plant diseases. Hence, there is a dire need to protect the plants against pathogens that bring about losses in the productivity and destruction to plant life. The basis for plant protection is a practical approach by educating on the type of phytopathogenic organisms, understanding host-pathogen relationship, conditions of disease initiation, methods of plant protection and methods of evaluation of pathogenicity. Phytopathogenic organisms are mostly viruses, viroids, phytoplasmas, bacteria, fungi, protists and higher plants.
Indirect methods of plant protection include cultural practices, quarantine and breeding methods. Direct methods of plant protection include- physical, mechanical, chemical, biological and biotechnical methods.
Physical methods of plant protection include- heating, treating by hot water, steaming of substrate and solarization
Mechanical methods include- handpicking or shaking off the pests, using of oil sprays (suffocation of pests).
Chemical methods is mostly by treating with pesticides as fungicides, bactericides, insecticides, herbicides, rodenticides, acaricides, molluscicides.
Biological control means using a living organism to suppress the population density of another organism to alter its virulence. There are synergistic, antagonist and parasitic type of biological control that is used in plant protection. Also, some insects, bacteria, fungi, nematodes and fungi are targeted against specific species or order of pathogens as biological control.
Biotechnical methods of plant protection is by- using pheromones (using hormones of female insects to sexually attract opposite sex), transgenic plants, induced resistance and gene editing.
Of these other plant pathogens, plant viruses are of high importance because it is a challenging process to treat or eliminate the infected plants. Virus diseases bring about economic losses to the plant. Plants contain various defence systems against viruses, such as RNA silencing and hypersensitive response which the virus must overcome to establish a successful infection.
The replication of many viruses takes place in association with particular cell organelles, and therefore recognition of a particular organelle or site within the cell by a virus. A single virus has a various types of host range i.e., one virus shall affect different. There are possibilities where multiple viruses can affect the same plant. Identification of pathogenic disease is highly important as control measures. Infection symptoms necessarily does not develop with viral interactions on the plant. Variation in vegetation and climatic factors bring about major challenges in the identification of symptoms in the plant.
Some macroscopic symptoms include- Necrotic symptoms, Loss of pigments, Ring spots in the plant. Some viruses show no symptoms unless subjected to ethanol treatment. Systemic symptoms: Stunting, dwarfing, reduction in leaf size, mosaic pattern, pigment difference- yellow, green or pale white, vein banding, Streak patterns, stripe disease, breaking in petal colour, Mottling of seed coat, yellowing or reddening of leaves, Upward leaf rolling, or downward leaf rolling, Ringspot disease, wilting etc.,
Viruses are usually transmitted by Vegetative propagation, mechanically, pollen and seeds, dodder and by vectors- insects, mites and nematodes (invertebrates), fungi and protists.
Detection and determination of viruses can be done based on symptoms, indicator plants, electron microscope, serological tests (ELISA- Enzyme Linked Immuno Sorbent Assay, precipitation tests, agglutination tests), molecular methods (PCR- Polymerase Chain Reaction), next generation sequencing (NGS).
Protection against viruses can be achieved by the following methods- Legislative, Prognosis of Occurrence, Agrotechnics (Cultural Practice), Cross Protection, Elimination of Viruses From Plants, Fight against Vectors, Breeding, Induced Resistance, Transgenic Plants, Gene Editing (Eg. CRISPR).
Besides being a destructive pathogen, some forms of plant viruses can also be useful as edible vaccines, biological agents and used as vectors for plant transformations.
