From Seed to Seed:
Plant Science for K-8 Educators

Disease-Causing Microbes. There's no doubt about it, microbes-fungi, bacteria, viruses, and others-can wreak havoc on both plants and people. Perhaps the best-or worst-examples of this fact are the potato famines that occurred in Ireland in the 1800s. To say that potatoes were a staple food for the Irish is an understatement. For many, potatoes were the only food. During the famine of 1845 through 1847, more than one million people died of starvation, and millions more emigrated to the United States, mainland Britain, and Australia-all because of a microbe named Phytophthora infestans. This fungus caused the disease that wiped out virtually the entire potato crop in Ireland in the summer of 1846. You may have already figured this out, but this subject provides a great opportunity to incorporate history into your botany lesson.

When a microbe causes disease in an organism, it is called a pathogen (Gr. pathos = suffering, genesis = beginning). The disease responsible for destroying the potatoes in Ireland is just one of the many plant diseases caused by microbes. Pathogens have been found to cause infection in many plants. In fact, fungi, bacteria, and viruses cause most of the diseases that you are likely to come across in the schoolyard garden or greenhouse. This is why it is so important to remove diseased or dead plant material from the garden-to prevent the further spread of disease by pathogens.

To sum things up: Not all microbes cause harm, and not all are harmless either.

Next, we'll look at some plant-insect relationships.

Would you like to know more?
Additional Online Resources

• The University of Michigan Herbarium: Fun Facts About Fungi-Additional information and activities on fungi.
  www.herb.lsa.umich.edu/kidpage/factindx.htm