Final answer:
Necrotrophic pathogens initially keep plants alive and then kill cells during their lifecycle.
Step-by-step explanation:
The pathogen that keeps plants alive initially and then kills cells during its lifecycle is called Necrotrophic pathogens.
Necrotrophic pathogens are predators that kill plants and then consume them. They produce toxins that kill cells or produce chemicals that plug the xylem tissue, preventing water transport and eventually killing the plant.
Examples of Necrotrophic pathogens include Pythium, a water mold, and ascomycete fungi that cause diseases like dutch elm disease and wilt diseases in tomatoes.