What are signs of plant disease that indicate identifiable structures of the pathogen?

Identifiable structures of a pathogen within a plant can be observed through specific signs that reflect the presence of diseases caused by various organisms. Fungal spores, bacterial ooze, and parts of parasitic plants are all direct indicators that provide evidence of a particular pathogen's presence.

Fungal spores can be seen on the surface of leaves or within the plant tissue, indicating a fungal infection. This can often manifest as powdery residues or specific fruiting bodies. Bacterial ooze is another sign, typically associated with bacterial infections, where a watery, often discolored substance may be found leaking from infected plant tissues. Additionally, parts of parasitic plants, such as dodder or broomrape, can directly indicate their presence, as they attach to host plants and can visibly alter their appearance.

In contrast, the other options describe symptoms of plant disease (like brown spots or leaf drop) or general conditions (like root rot) that do not specifically showcase the identifiable structures of pathogens. Symptoms may suggest a problem but do not provide the clear, direct evidence of the pathogen's identity that the correct choice does.