Plant Viruses
Although we didn’t realize it at the time when COVID first appeared, many gardeners especially vegetable gardeners, already had a good deal of knowledge on coping with viruses. Planting immune varieties and crop rotations are just a few ways we kept plant viruses from spreading between plants.
Planting vegetables at enough distance to allow air flow is very similar to the six-foot distance rule used during the pandemic.
Viruses are intracellular (inside cells) pathogenic particles that infect other living organisms. Human diseases caused by viruses include chickenpox, influenza, rabies, small pox and COVID.
Although these are viruses most of us are familiar with, the first virus ever described in scientific terms was a plant virus. Discovered by Martinus W. Beijerinck, a Dutch microbiologist, in 1898. Gardeners and farmers know it as Tobacco mosaic virus or TMV and avoid planting related crops in their fields to prevent spread. The term virus was derived from the original description of the causal agent of TMV—“contagium vivum fluidum” or contagious living fluid.
Virus particles are extremely small and can be seen only with an electron microscope. Organisms that transmit pathogens are called vectors. Human and insect vector transmission are the two most important means by which plant viruses spread. The activity of humans in propagating plants by budding and grafting or by cuttings is one of the chief ways viral diseases spread.
Viruses are ‘obligate parasites’, meaning they require a living host (cell) in order to grow and multiply. Interestingly, many kinds of plants are infected with viruses and show no symptoms. Such infections are referred to as being latent.
Viruses are difficult to classify and, for lack of anything better, they were given descriptive (and sometimes colorful) names based on the disease they cause for example, tobacco ring spot, potato leaf roll, tomato spotted wilt.
Once plants are infected, little can be done to free them from the virus.
Since different cultivars and species show different degrees of resistance to some viruses, resistant types should be planted whenever they are available. Recent advances in plant cell molecular biology and virology have led to the development of genetically modified plants with superior resistance to some viruses.
There are numerous cultural practices that can be used to reduce plant losses due to virus infection:
- Scouting and removal of infected plants.
- For cutting or propagating seedlings use cleaner or sanitized tools and equipment with alcohol or 10% bleach solution.
- Rotations to non-host crops.
- The isolation of newly received plants prior to their introduction into your garden.
- There are other precautions used by large scale industry.
- There are no chemical sprays or biological control approaches to eradicate viruses.
*Information in this article are from Ohio State University Fact sheet
‘VIRUAL DISEASES OF PLANTS’
Sarah D. Williams, Michael J. Boehm, and Feng Qu,
Department of Plant Pathology
Happy Spring Gardening,
James
