The disease damping off seedlings during nursery stage is caused by the pathogen

The disease damping off seedlings during the nursery stage is caused by the pathogens Pythium aphanidermatum and Pythium debaryanum.
Damping off is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.
Damping off is caused by several soil-borne fungi and fungus-like organisms including Pythium, Phytophthora, Rhizoctonia, and Fusarium, which infect seedlings and cause them to 'damp off' or collapse and decay.