Final answer:
Plant diseases are caused by pathogens such as bacteria, fungi, and viruses. The late blight of potato, caused by Phytophthora infestans, is a historic example. Pathogens spread through contaminated material, wind, water, and vectors.
Step-by-step explanation:
The pathogens that cause diseases in plants include a broad range of organisms such as bacteria, fungi, water molds, nematodes, and viruses. These pathogens can lead to disorders in plants due to various interactions with the plant's environment and genetic make-up. One of the most notable diseases caused by these pathogens is the late blight of potato, which is caused by the water mold Phytophthora infestans. This particular pathogen was responsible for the Irish Potato Famine and requires specific environmental conditions to thrive, namely, cool and moist environments.
Pathogens spread in a number of ways, including through the movement of contaminated soil or plant material, wind, water, and by vectors such as insects. Human activity, such as the transport of infected plants, also contributes to the spread of these pathogens. Additionally, certain practices like monoculture make crops more susceptible to outbreaks, as seen with the Irish Potato Famine. Effective management of plant diseases requires understanding the disease triangle, which consists of a susceptible host, a pathogen, and an environment conducive to the disease.