How does horizontal resistance differ from vertical resistance?

Horizontal resistance is characterized by its ability to provide broad protection against multiple pathogens, which is why it is the correct choice. This form of resistance typically involves a range of defense mechanisms that plants can employ against various pathogens, making them less vulnerable to infection from a wide array of microorganisms. This broad-spectrum capability is particularly beneficial in maintaining plant health across different environmental conditions and diverse pathogen challenges.

In contrast, vertical resistance is more specific and typically effective against a single or limited number of closely related pathogens. This specificity can lead to strong defenses, but it might not protect the plant against other pathogen species. Although vertical resistance can be very effective under certain conditions, the narrow scope can leave plants exposed to other pathogens not covered by that specific resistance mechanism.

The mention of overall effectiveness in vertical resistance doesn't consider the context in which each type of resistance operates. Horizontal resistance encourages the development of crops that are resilient in varying conditions due to their enhanced ability to combat a larger range of pathogens.