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Oospores of Hyaloperonospora parasitica, agent of the downy mildew (in the middle)

An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes.[1] They are believed to have evolved either through the fusion of two species or the chemically-induced stimulation of mycelia, leading to oospore formation.[2]

In Oomycetes, oospores can also result from asexual reproduction, by apomixis. These are found in Fungi as sexual spores which help the sexual reproduction of Fungi. These haploid, non motile spores are the site of meiosis and karyogamy in oomycetes.[3]

A dormant oospore, when observed under an electron microscope has led researchers to draw conclusion that there is only a single central globule with other storage bodies surrounding it.[4]


  1. ^ Tronsmo, Anne, M. (2020). Plant Pathology and Plant Disease. CABI. ISBN 1789243173.
  2. ^ Uchida, J. Y.; Aragaki, M. (1980). "Chemical Stimulation of Oospore Formation in Phytophthora capsici". Mycologia. 72 (6): 1103. doi:10.2307/3759563. JSTOR 3759563.
  3. ^ Fry, William, E. "Introduction to Oomycetes". American Phytopathological Society. Retrieved 29 March 2021.
  4. ^ Ruben, D.M (May 1978). "Ultrastructure of Oospore Germination in Pythiumaphanidermatum". JSTOR. doi:10.2307/2442581. Retrieved 2021-04-04.