Which of the following pathogens is commonly found in irrigation water?

Pythium is the correct answer because it is a water mold known for thriving in aquatic environments, particularly in irrigation water. This pathogen is responsible for various plant diseases, especially root rot, and is commonly found in soil and water that is conducive to its growth. Pythium spores can easily spread through irrigation systems, making it a prevalent pathogen in agricultural settings where overhead irrigation is used.

In contrast, while Fusarium is also a significant plant pathogen, it typically resides in the soil rather than in water, and it is more associated with soilborne diseases. Verticillium, likewise, is primarily a soilborne pathogen and does not commonly interact with irrigation water. Anthracnose is caused by a group of fungi that usually thrive on plant surfaces rather than in water. The characteristics of Pythium enable it to proliferate in moist environments, making it the most likely pathogen to be found in irrigation water.