What is the key characteristic of local system fungicides?

Local system fungicides are characterized by their ability to penetrate into plant tissues but primarily move through the xylem, providing protection to the parts of the plant that are accessible through that vascular system. This characteristic allows them to offer some systemic action, helping to control fungal pathogens that may infect the plant.

The focus on movement through the xylem is significant because it differentiates these fungicides from those that purely act on the surface. Local system fungicides can create a more thorough defense against infections by affecting not just the exposed surfaces but also areas within the plant that might be susceptible to disease.

Other options, such as those suggesting that fungicides act on the surface only, do not capture the systemic nature of local system fungicides, while promoting flowering is unrelated to the function of fungicides and highlights a misunderstanding of their purpose in plant health management.