Microbes include many different organisms like bacteria, archea, protists, algae, fungi and viruses. You can find more information on this cute page about microbiology. The main plant pathogens are fungi, bacteria, protists and viruses.
- Viruses are the smallest microbes. They are unique because they cannot survive on their own. (That’s why there is a debate about whether they are living creatures or not.)
- Bacteria are single cell organisms without a nucleus. Their cell structure is simpler than that of other organisms as there is no nucleus that contains their genetic material.
- Archaea were long considered to be bacteria. They live in extreme environments such as hot springs and can exist as single cells, as filaments or clusters.
- Protists are single cell organisms with a nucleus, a good deal bigger than bacteria. They come in many different shapes and size. They live in moist habitats including fresh water, marine environments and the soil. Some devastating plant pathogens such as potato blight are protists.
- Algae can exist as single cells or joined together in chains or made up of many cells. Most algae live in fresh or seawater where they can either be free-floating (planktonic) or attached to the bottom.
- Fungi are single-celled or very complex multi-cellular organisms. Most fungi live on the land, mainly in soil or on plant material. Their shape ranges from single celled baker’s yeast to the beautiful red-white-dotted-fruiting bodies of the death cap mushroom.