What part of infected plants do smut fungi eventually cover?

Smut fungi are known for their distinctive lifecycle that typically results in the formation of spores in the parts of the plant that are most conducive to reproduction. When plants are infected by these fungi, the reproductive structures often manifest as dark, spore-filled galls that replace the normal leaves, kernels, or flowers of the host plant. In many crop species, particularly cereals, this type of infection leads to significant damage and economic loss, as the kernels can be transformed into masses of fungal spores, significantly affecting yield.

The leaves and kernels are specifically vulnerable because that’s where the fungal development can take advantage of the plant's biomass. The spore formation in these parts not only serves as a means for the fungus to spread but also signifies the infection's severity, causing stunted growth and reducing the plant's viability. Thus, the final answer regarding the part of infected plants covered by smut fungi correctly identifies leaves or kernels as the primary targets, highlighting the agricultural implications and the ecological roles these fungi play.