What is the sexual structure associated with the life cycle of downy mildew in lettuce?

The sexual structure associated with the life cycle of downy mildew in lettuce is oospores. Downy mildew is caused by the pathogen Bremia lactucae, which is a water mold. In its life cycle, oospores are formed during sexual reproduction when two compatible mating types come into contact. These oospores are thick-walled and can survive unfavorable environmental conditions, allowing the pathogen to persist in the soil or plant debris to initiate infections in subsequent growing seasons.

While conidia and sporangia are also important structures in the life cycle of downy mildew, they are asexual reproductive structures. Sporangia can produce new spores that can infect plants rapidly, but they do not contribute to sexual reproduction. Mycelium refers to the vegetative part of the fungus and is not a sexual reproductive structure. Thus, oospores are specifically the correct answer when discussing the sexual reproductive phase in the lifecycle of downy mildew.