Which of the following is true regarding systemic fungicides?

Systemic fungicides are designed to be absorbed and transported throughout the plant tissues. This characteristic allows them to provide protection not just to the infected areas but also to other parts of the plant that may not have been treated directly. This systemic action is particularly beneficial because it enables the fungicide to target pathogens that may reside within the plant's tissues, which surface-applied fungicides would not effectively reach.

The ability of systemic fungicides to move within the plant makes them effective against diseases that can spread systemically, as they can inhibit the growth of the pathogen wherever it may be located within the plant. Their effectiveness can persist even after application, providing ongoing protection against future infections.

While other statements touch on various aspects of fungicide efficacy, they do not accurately reflect the systemic nature of these compounds. For instance, systemic fungicides are not limited to surface action; they can be effective both before and after symptoms appear, depending on the type and timing of application. Additionally, while certain fungicides may enhance a plant’s resistance to pathogens, that is not a universal action of systemic fungicides, making the key feature of their capability to spread throughout the host plant the most pertinent statement.