page_title: Phytophthora
section_title: Biology
hierarchical_section_title: Phytophthora / Biology
caption_attribution_description: Reproductive Structures of the Phytophthora. The asexual (A) sporangia, (B) zoospores, and (C) chlamydospores, and the sexual (D) oospores.
context_page_description: Phytophthora is a genus of plant-damaging oomycetes, whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The cell wall of Phytophthora is made up of cellulose. The genus was first described by Heinrich Anton de Bary in 1875. Approximately 170 species have been described, although 100–500 undiscovered Phytophthora species are estimated to exist.
context_section_description: Phytophthora species may reproduce sexually or asexually. In many species, sexual structures have never been observed, or have only been observed in laboratory matings. In homothallic species, sexual structures occur in single culture.  Heterothallic species have mating strains, designated as A1 and A2. When mated, antheridia introduce gametes into oogonia, either by the oogonium passing through the antheridium (amphigyny) or by the antheridium attaching to the proximal (lower) half of the oogonium (paragyny), and the union producing oospores.  Like animals, but not like most true fungi, meiosis is gametic, and somatic nuclei are diploid.
  Asexual (mitotic) spore types are chlamydospores, and sporangia which produce zoospores.  Chlamydospores are usually spherical and pigmented, and may have a thickened cell wall to aid in their role as a survival structure.  Sporangia may be retained by the subtending hyphae (noncaducous) or be shed readily by wind or water tension (caducous) acting as dispersal structures.  Also, sporangia may release zoospores, which have two unlike flagella which they use to swim towards a host plant.
caption: Phytophthora forms: A: Sporangia. B: Zoospore. C: Chlamydospore. D: Oospore
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