What is a biotroph?

A biotroph is best defined as a parasite that cannot survive in a dead host and keeps it alive. This characteristic highlights the biotrophic lifestyle, where the parasite depends entirely on a living organism for survival and reproduction. Biotrophic pathogens extract nutrients from their hosts without necessarily killing them right away, which can result in prolonged infection and can lead to symptoms associated with decreased vigor in the host plant.

This option accurately reflects the fundamental relationship between biotrophs and their hosts, emphasizing the necessity of a living host for their life cycle. Unlike other types of parasites, such as necrotrophs, which can thrive on dead organic matter and often kill their hosts, biotrophs rely on sustaining the host for their own continued existence.

The other choices imply different survival strategies and host interactions that are characteristic of either necrotrophic or saprophytic organisms, rather than biotrophic ones.