Which of the following is NOT a factor required for infection to occur in plants?

The presence of excessive nutrients is not a factor required for infection to occur in plants. For an infection to take place, several specific conditions must be met, including the presence of a pathogen (the organism), a favorable environment for that pathogen to thrive, and a susceptible host that can support the pathogen's life cycle.

While nutrients play a role in plant health and can affect overall vigor, excessive nutrients do not directly lead to infections. In fact, too much of certain nutrients can lead to plant stress or other issues, which might even make a plant more resistant to certain infections. Therefore, it's the other three factors—pathogen presence, environmental conditions, and host susceptibility—that are critical for the initiation of an infection in plants.