How Do Viruses Spread in Plants?

Plant viruses can cause tremendous losses in crop production in every region of the world. Because plant cells have a robust cell wall, viruses can't penetrate them without help. There are various ways viruses can infect plants. Although most plant viruses are carried by a vector organism, such as insects that feed on the plant, viruses can also be spread through wounds made during cultural procedures such as pruning or grafting in the field or greenhouse. Vegetative propagation, as well as mechanical inoculations done by humans, are other ways that plant viruses can be introduced or spread. However, insects most often spread viruses to plants.

Non-propagative transmission is the process of insects carrying viruses to hosts by biting or sucking plant tissues. Sometimes the vector both distributes the virus as well as intensifies the infection. Insects can carry viruses from one plant to another by feeding. Some of the main insects that transfer viruses to plants include aphids, whiteflies, leafhoppers, beetles and mites.

Various groups of living organisms can serve as vectors, spreading viruses from plant to plant such as bacteria, fungi, and nematodes. About 200 kinds of bacteria can infect plants with viruses. It's in humid, warm climates that you see most of their destruction. Fungal spores are tiny and light, traveling long distances through air to contaminate other plants. Nematodes, which are microscopic worms and the most abundant multi-cellular animals on earth, can serve as vectors for spreading viruses from plant to plant.

Plant viruses can spread by mechanical transference, such as sap being transferred from a wounded plant to a healthy one. Usually contact happens during agricultural procedures. Virus-infected sap can accidentally spread from tools, hands or clothing, infecting plants. Cucumber and potato viruses are some of the most common viruses spread by sap.

Seeds can sometimes carry virus infection because of external contamination or by an infection of the embryo's living tissues. This leads to new crops breaking out in disease, which is at first only local in circulation. However, infection can spread to the rest of the crop by mechanical means.

Grafting or vegetative propagation is a means of increasing vegetation. Although grafting methods are cheap and simple ways to grow plants, they're also a common cause of plant viruses. Viruses can also develop and multiply from contaminated buds, cuttings and rootstocks, so it's necessary to use only certified virus-free grafting or budding stock.

Spreading viruses by mechanical means is the most commonly used method for doing experimental plant infection. It's normally done by rubbing preparations containing a virus onto leaves which are most likely to be infected. Virus particles can infect soil for a long time and be carried to leaves of new hosts by wind or rain-splashing mud.