Oomyceter

Oomycetes, also called oomyceters, are a group of fungus-like eukaryotes within the Stramenopiles. Although they resemble fungi in habit and ecological role, they are not true fungi; they are more closely related to brown algae and diatoms. Oomycetes include many plant and animal pathogens as well as saprotrophs. Major genera include Phytophthora, Pythium, Saprolegnia, and Albugo.

They form filaments (hyphae) that are coenocytic (non-septate) and have cell walls rich in cellulose and glucans, not chitin. They are absorptive heterotrophs, obtaining nutrients by secreting enzymes and absorbing dissolved organic matter.

Asexual reproduction occurs via sporangia that release motile zoospores equipped with two unequal flagella; these zoospores swim to new substrates. Sexual reproduction typically involves oogamy, with oogonia and antheridia forming thick-walled oospores that can persist in the environment.

Many oomycetes inhabit moist or aquatic environments and exhibit a wide range of lifestyles, from saprophytes to aggressive pathogens. Some species have complex life cycles that enable rapid dispersal and persistence in plant tissues.

Economic and ecological significance: several species are major plant pathogens, causing potato late blight (Phytophthora infestans), sudden oak death (Phytophthora ramorum), damping-off in seedlings (Pythium spp.), and downy mildews (Peronosporales). Management relies on sanitation, resistant cultivars, crop rotation, drainage, and targeted fungicides.