Question

what is a sign in plant disease diagnosis?
wilting due to drought
stunted growth from poor soil
leaf curling from viruses
visible fungal growth on a leaf

Explanation:

In plant disease diagnosis, a "sign" refers to the actual presence of the pathogen or its structures on the plant. Among the options, "Visible fungal growth on a leaf" is a sign as it directly shows the pathogen (fungal structures). The other options (wilting due to drought, stunted growth from poor soil, leaf curling from viruses) are symptoms (plant's response to stress or pathogen, not the pathogen itself).

Answer:

Visible fungal growth on a leaf