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How Pathogens Infect Plants

An unidentified culture.

Pathogens are disease-causing organisms usually in the group of microscopic biotic agents. These organisms can survive all over the environment – air, water, soil and even on the surface of seeds and transplants.

Different varieties of crop plants have different levels of tolerance and infection-preventing capacity against these pathogens. However, in conducive environments – when temperatures are 68° to 77° F and foliage remains wet due to rain or overhead irrigation, followed by high relative humidity or cloudiness – these pathogens can infect plant parts. Here’s a little bit more about how different pathogens can infect plants, causing them to get sick and sometimes die.

When spores of fungal pathogens from a remote or local source come in contact of a healthy plant, they can germinate on water droplets and forcefully invade the plant through the epidermal cell layers.

Bacterial cells, when disseminated by air or water droplets on a healthy plant, can take advantage of the plant’s natural openings or wounds caused by other factors to get inside.

Insects usually facilitate infection of a plant with virus particles when they feed on an infected host plant and then feed on an uninfected plant. In some cases, mechanical transmission also can occur.

Plant parasitic nematodes are microscopic worms that normally inhabit the soil. From the soil, endoparasites forcibly enter the roots and feed on interior tissues, while ectoparasites create a feeding site on the plant’s root from the outside.

By Mahfuz Rahman, WVU Extension Service Specialist – Plant Pathology