Bracteoles (leaf- like structures) slightly longer than the oospore. The species is monoecious and richly fertile oogonia are situated above the antheridia. The oospore is dark brown or black.
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The product of the union of an antherozoid and an oosphere is termed an oospore.
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An oogonium can be likened to a female reproductive organ while an antheridium carries out the role of a male reproductive organ. The penetration of an oogonium via an antheridium leads to the formation of a sexual spore or an oospore. The oospore will overwinter and germinate to produce infectious sporangia once conditions improve.
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The oospore on germination usually gives origin to a zoosporangium, but may form directly a germ tube which infects the host.
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"Chemical Stimulation of oospore formation in Phytophthoracapsici". Mycologia 72, 1103-1108. Initial responses to infection include production of radical oxygen species, including H2O2.
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This oospore will function as a survival structure for the pathogen over the winter, and serve as the primary inoculum the following spring.
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Symptoms of this pathogen include necrosis in the roots, chlorosis, and wilting. Phytophthora cactorum can be identified by examining oogonia, antheridium, oospore, and sporangia structure.
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Like all the other species in its genus, Albugo occidentalis is an oomycete. The survival structure is an oospore, which is the result of the karyogamy of two haploid gametes (the oogonium and antheridium). The oospore can overwinter in the soil, and in the spring it produces zoospores which will encyst on the surface of spinach leaves in the presence of water and germinate. Asexual propagation of Albugo occidentalis occurs via the production of sporangia on sporangiophores.
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The oospore apical cell divides to produce the protonemal initial, from which the primary protonema arises, and the rhizoidal initial, from which the primary rhizoid descends. From these the alga continues its development.
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After several steps of differentiation and meiosis, an oospore, the primary survival structure, is formed. These thick-walled oospores can remain dormant for many months, and will eventually germinate through two methods. A sporangium can be produced, which generates a cyst and releases zoospores, or the oospore can create a germ tube which can directly penetrate and infect a host. This disease cycle is extremely dependent on water for dispersal, making greenhouses, irrigation systems, and hydroponics especially prone to spread of P. dissotocum.
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In a common mode of fertilization found in certain species of Thallophytes, the antheridia will bind with the oogonia. The antheridia will then form fertilization tubes connecting the antheridial cytoplasm with each oosphere within the oogonia. A haploid nucleus (gamete) from the antheridium will then be transferred through the fertilization tube into the oosphere, and fuse with the oosphere’s haploid nucleus forming a diploid oospore. The oospore is then ready to germinate and develop into an adult diploid somatic stage.
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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. They are believed to have evolved either through the fusion of two species or the chemically- induced stimulation of mycelia, leading to oospore formation. In Oomycetes, oospores can also result from asexual reproduction, by apomixis. These are found in Fungi as the sexual spores; these help in the sexual reproduction of Fungi.
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In this case the two types of sex organs usually arise from different points on the lateral branches. All cells of the Charales are haploid except for the fertilized zygote, the large single cell in the interior of the oogonium, which becomes enclosed in a thickened hard wall to form an oospore that awaits favorable conditions for germination. Upon germination the diploid oospore undergoes meiosis, producing four haploid nuclei. A septum divides a small apical cell with one haploid nucleus from a large basal cell containing the other three nuclei, which will slowly degenerate.
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The pathogen grows throughout the plant, infecting the leaves as they grow, leading to chlorosis. The chlorotic leaves develop white streaks. These white streaks are the location of oospore production. This only occurs in plants that were systemically infected as a seedling.
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Spring, O. and Zipper, R. (2000) Isolation of oospores of sunflower downy mildew, Plasmopara halstedii, and microscopical studies on oospore germination. J. Phytopathol. 148, 227–231. After primary infection, zoospores serve as a main source of inoculum throughout the rest of the season.
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56, 209–218. Oospores have the potential to live in soil up to 8 years, while oospore germination takes 10–30 days. Germination length depends on environmental condition and typically occurs in the spring. The germinating oospores form sporangia that release motile zoospores as a secondary inoculum.
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Thick-walled sexual spores, called oospores are produced which germinate, producing either vesicles inside the plant tissue, exit tubes with vesicles at the tip, or germ tubes. Further zoospores develop inside the vesicles. The infection is spread by either oospore-infected seed or by mechanical movement of sporangia.
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A sexual stage also exists for P. humuli, in which an antheridium fertilizes an oogonium to produce a recombinant oospore. While oospores are classically thought to be the chief survival structure of oomycetes, their role in primary infection in downy mildew of hops is uncertain.Johson, D.A., et al. 2009. Downy mildew.
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The disease is primarily a root rot that causes symptoms of foliar blight. Sporangia are produced on the mycelium and can produce zoospores for asexual reproduction or an oogonium and antheridium for sexual reproduction. Once the oogonium is fertilized, the oospore either infects via germ tube or produces sporangia and zoospores.
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Diasporangium is a genus of water moulds. It contains the single species Diasporangium jonesianum, described in 1936 by German mycologist Willy Höhnk. Known from the United States and Germany, where it grows in soil, D. jonesianum can cause root rot in various plants. It has a spherical oogonium up to 25 µm in diameter, with an oospore that almost fills the oogonium.
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Once infection season comes to an end, sexual reproduction occurs to form an oospore. In order to have successful sexual reproduction, weather conditions must be favorable and mating types must match. Two mating types, A1 and A2, exist for Phytophthora colocasiae. Hormonal signaling allows for sporangia of the two mating types to come together and initiate the development of oogonia and antheridia.
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Peronospora manshurica commonly begins its disease cycle in the spring, with overwintering oospores mainly serving as the primary inoculum. This primarily occurs by the use of oospore encrusted seeds for planting. Oospores, and sometimes even mycelium, surviving on plant material can also serve as the primary inoculum. After the first infection by the oospores, the secondary dispersal of infection is accomplished by conidia originating from conidiophores.
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Studies in Sicily have shown optimum time for oospore germination is between the end of February and the middle of March.(Burruano and Ciofalo, 1990) With this understanding, if fungicides are used just before optimum conditions occur, they have proven to be an effective control method of the pathogen. Other control methods include proper watering, and a good location where the plant can receive continual sunlight.
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Oomycota or oomycetes () form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result of contact between hyphae of male antheridia and female oogonia; these spores can overwinter and are known as resting spores. Asexual reproduction involves the formation of chlamydospores and sporangia, producing motile zoospores.
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Phytophthora zoospores require water to germinate from the oospore, and can migrate by themselves through waterlogged soil. P. cinnamomi zoospores remain mobile for up to 10 hours, and can swim at speeds of up to 58 centimetres per hour. However, their direction of travel frequently changes, so they disperse no more than 6 cm by swimming. Consequently, long-distance dispersal of Phytophthora depends on other forms of transport.
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The co-occurrence of the two mating types is significant due to the possibility of sexual recombination and formation of oospores, which can survive the winter. Only in Mexico and Scandinavia, however, is oospore formation thought to play a role in overwintering.Lehtinen A, Hannukkala A. (2004) Oospores of Phytophthora infestans in soil provide an important new source of primary inoculum in Finland. Agricultural and Food Science 13:399–410.
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The Charales grow in freshwater and brackish environments worldwide, and have large, macroscopic thalli growing up to 120 cm long, they are branched, multicellular, and use chlorophyll to photosynthesize. Their only diploid stage in the life cycle is the unicellular oospore. They may be called stoneworts, because the plants can become encrusted in lime (calcium carbonate) after some time. The "stem" is actually a central stalk consisting of giant, multinucleated cells.
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McGraw-Hill Book Company In Oomycota and some other organisms, the female oogonia, and the male equivalent antheridia, are a result of sexual sporulation, i.e. the development of structures within which meiosis will occur. The haploid nuclei (gametes) are formed by meiosis within the antheridia and oogonia, and when fertilization occurs, a diploid oospore is produced which will eventually germinate into the diploid somatic stage of the thallophyte life cycle. In many algae (e.g.
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The cell walls are composed of cellulose, though there may be also a superficial layer of a more gelatinous material of unknown composition. The storage material is starch, except in the oospore, where oil also occurs. This starch also accumulates in special storage structures, termed bulbils, which consist of rounded cells of varying size which are developed in clusters on the lower stem and root nodes. They are mainly developed when the algae are growing in fine slimy mud.
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Phytophthora kernoviae can survive as an oospore, a thick walled resting structure and has been found to survive on infected plant tissues and in soil. Chlamydospores, long term resting structures that are seen in Phytophthora ramorum and other Phytophthora species are not observed in Phytophthora kernoviae. Production of sporangia, oospores, and zoospores were observed on Phytophthora kernoviae. Sporangia are only formed on hosts with susceptible foliage, trunk cankers have not exhibited sporulation and do not spread disease.
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This is why the pathogen is most severe in summer and autumn-harvested crops. The pathogen overwinters in the form of an oospore, which can survive several years in the soil and inoculates the host when temperatures become optimal. In heavy moisture and wet soil, the pathogen can also release zoospores that can further increase its population up to 1000-fold. Flooding of soil by heavy rains as well as poorly drained soils have been shown to increase cavity spot disease development.
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The mycelium grows intracellularly and haustoria penetrate through the host cells when the temperature is around 60 degrees F. After about 1–2 weeks when the temperature is between 60-64 degrees F, conidiophores (the asexual stage) will form out of the plant stomata bearing conidia. Sporulation occurs at night. The conidia disseminate in high humidity mornings when it’s about 50-60 degrees. Meanwhile during the sexual stage, the antheridia (the male sex organ) fertilizes the oogonium (the female sex organ) with a fertilization tube and an oospore is developed.
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The pathogen Aphanomycete cochlioides, like most oomycete fungi, survives and overwinter as oospores in plant debris or soil. When the soil warms in the spring the oospores receive signals to germinate. The oospores have the ability to directly infect the root in the soil but it is more common for the oospore to play a smaller role in the life cycle producing a specialized hyphae called sporangium. The sporangium has the ability to produce zoospores- which have two different types of flagella, tinsel and whiplash, that allow them to be motile in soil water.
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A variety of cultural controls are effective against sorghum downy mildew. In areas where oospores are the principal source of inoculum, such as in the United States, crop rotation is an effective strategy, as oospores will be stimulated to germinate by both host and non- host crops, but will not be able to infect plants apart from corn, sorghum, and Johnson grass. Flax (Linum usitatissimum) is an example of a trap crop that is used to reduce the amount of oospore inoculum in the soil, before planting a susceptible crop like sorghum or maize. Deep tillage also reduces the amount of oospores surviving in the soil and therefore the incidence of the disease.
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