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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 978-1789243178.{{cite book}}: CS1 maint: multiple names: authors list (link)
  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.{{cite web}}: CS1 maint: multiple names: authors list (link)
  4. ^ Ruben, D.M (May 1978). "Ultrastructure of Oospore Germination in Pythiumaphanidermatum". American Journal of Botany. 65 (5): 491–501. doi:10.2307/2442581. JSTOR 2442581. Retrieved 2021-04-04.