While this pathogen enters through the leaf, the disease is caused by root rot that causes symptoms of foliar blight. The mycelium gives rise to chlamydospores and oospores. Oospores produce mycelium that produce sporangia. Oospores are the survival structure of P. cactorum.
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P. fragariae survives in the soil in the form of oospores. These oospores can survive for up to 4 years; there are some reports of spores remaining viable 13 – 15 years. The oospores germinate to form usually one sporangia. Sporangia germinate in the presence of water to release motile zoospores.
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P. colocasiae is an oomycete and is thus characterized by oospores and coenocytic hyphae. Oospores have very thick-walls which provide durable survival structures. As a result, oospores overwinter in soil, underground storage organs, or on leaf debris left in the field after harvest. However, inoculum does not survive for very long on leaf tissue.
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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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Apomixis can apparently occur in Phytophthora, an oomycete. Oospores from an experimental cross were germinated, and some of the progeny were genetically identical to one or other parent, implying that meiosis did not occur and the oospores developed by parthenogenesis.
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This creates a simple life cycle for Phytophthora kernoviae. Oospores can germinate and create mouse-shaped sporangia. Sporangia serve as dispersal structures and create and release Zoospores, motile infectious spores. Once released, oospores germinate on the host and infect target host tissues.
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The oospores are the main source of the primary inoculum of this disease. They are present in the soil when the host seedlings are germinating. The oospores then infect the roots of the seedlings. This type of infection is a systemic infection of the plant.
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Plasmopara halstedii infects sunflowers, producing oospores which can remain dormant in the soil for many years.
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They are often disseminated by wind. The oospores can overwinter in the soil and in the debris on the surface of the soil. The oospores have very thick walls, which makes them capable of surviving in the soil for years under many different weather conditions.Richard A. Frederlksen.
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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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Personosclerospora sorghi has a polycyclic disease cycle. It is capable of causing secondary infections of susceptible hosts throughout the growing season. Its resting structures, the structures that allow the pathogen to overwinter, are the oospores. These oospores are produced in the infected plants from the previous growing season.
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Oospores, on the other hand, can be spread across a field by water runoff, farming equipment, and workers.
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They also produce sexual spores, called oospores, that are translucent, double-walled, spherical structures used to survive adverse environmental conditions.
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This is a polycyclic pathogen with a sexual and an asexual stage. It thrives in cool moist environments. Over winter in the soil, oospores survive and wait for spring. In warmer conditions when it gets to about 47-53 degrees F the oospores will germinate and produce an appressorium or form a short germ tube.
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The antheridia will fuse to the oogonia, initiating plasmogamy and then karyogamy, and will result in the production of many oospores. The oospores can then be dispersed by the wind to infect more plants. Both Peronospora and Pseudoperonospora are characterized by their ability to produce melanized sporangia, but Pseudoperonospora produces zoospores whereas Peronospora cannot.
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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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When the oospores become mature, the white streaks on the leaves turn brown and become necrotic. These necrotic areas become shredded over time, which is how the mature oospores are disseminated. The spores are carried by the wind, and they become the source of inoculum in subsequent generations.C.H. Bock, M.J. Jeger, B.D.L. Fitt, and J. Sherington.
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Plasmopara viticola, the causal agent of grapevine downy mildew, is a heterothallic oomycete that overwinters as oospores in leaf litter and soil. In the spring, oospores germinate to produce macrosporangia, which under wet condition release zoospores. Zoospores are splashed by rain into the canopy, where they swim to and infect through stomata. After 7–10 days, yellow lesions appear on foliage.
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If the conditions in the leaf were unfavourable, the mould can undergo sexual reproduction and produce haploid antheridia and haploid oogonia through meiosis. These two structures are the only non-diploid stages of the Hyaloperonospora. The antheridia will fuse to the oogonia inducing plasmogamy followed by karyogamy to form diploid oospores. The oospores will then be dispersed through the wind to infect more plants.
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Diseased roots develop lesions that may spread up the stem and eventually kill the entire plant. Phytophthora sojae also produces oospores that can remain dormant in the soil over the winter, or longer, and germinate when conditions are favourable. Oospores may also be spread by animals or machinery. Phytophthora sojae is a diploid organism with a genome size of 95 Mbp (Millions of base pairs).
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White rust is an obligate parasite. This means it needs a living host to grow and reproduce. The Albuginaceae reproduce by producing both sexual spores (called oospores) and asexual spores (called sporangia) in a many-stage (polycyclic) disease cycle. The thick-walled oospores are the main overwintering structures, but the mycelium can also survive in conditions where all the plant material is not destroyed during the winter.
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After entering an area, the eradication of the pathogen is difficult due to the formation of oospores, which can remain viable in soil for many years.
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Phytophthora sojae overwinters in plant debris and soil as oospores. Oospores are made after the male gamete, antheridium, and female gamete, oogonium, undergo fertilization and then sexual recombination (meiosis). They possess thick cell walls with cellulose that enables them to survive harsh conditions in the soil without germinating for several years. They begin to germinate once the environmental condition is favorable during spring (see § Environment) and produce sporangia.
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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 fungus spreads by oospores on diseased leaves and/or on infected seed. The disease spreads in environments with high humidity and favors temperatures between 20-22 °C.
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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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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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It is also possible for oospores and mycelium to overwinter in the seeds of maize. The mycelium infects the scutellum of the seed. The oospores and mycelium that are present in the seed often lose their viability when the seeds are dried, but under the right circumstances, it is possible for these infected seeds to become a source of inoculum, infecting the maize plant as it grows. Infection of the seed itself often occurs with the plant that produced the seed had been infected later in development.
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Oospores are very sturdy and can remain stagnant in the soil for a long time and therefore crop rotation alone is not effective. Proper field drainage prevents flooding and therefore inhibit zoospore movement towards the host.
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Phytophthora bilorbang is a non-papillate homothallic plant pathogen known to infect Rubus anglocandicans (European blackberry) in Western Australia. It produces non-papillate sporangia, oogonia with smooth walls containing thick- walled oospores, as well as paragynous antheridia.
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The spores can also be transported by the wind, rain, insects, and even by people. At the end of the growing season, the pathogen overwinters by oospores that can be found in the soil or on plant debris.
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The pathogen persists as oospores in the soil, or on beet seed crops, or on overwintered volunteer beet plants. Attacks are most important at the seedling stage. The cotyledons are systemically infected, becoming discoloured and distorted. Loss of seedlings causes uneven crop development.
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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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Phytophthora sojae is considered to be a monocyclic pathogen and has one effective infection in its cycle. This is because the oospores don’t germinate together at the same time; rather they each have their own distinct favorable condition in which they’ll initiate their germination.
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In the latter case, the sporangia behave as conidia and are often referred to as such. Sexual reproduction is via oospores. The parasitised plants are angiosperms or gymnosperms, and most Peronosporaceae are pathogens of herbaceous dicots. Some downy mildew genera have a more restricted host range, e.g.
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Peronospora manshurica can cause systemic infection. This predominantly occurs when seeds and surrounding soil contain oospores, causing seedling hypocotyls to be infected upon germination. Systemic infection can also occur during a dense secondary dispersal of inoculum, when newly formed leaves are infected right after their formation.
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Plasmopara halstedii is a plant pathogen infecting sunflowers. The species is one of many pathogens commonly referred to as downy mildew. P. halstedii originated in North America. Plasmopara halstedii oospores produce a thin wall which are resistant structures, sexually produced that are essential for its continuation.
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The optimum temperature range for P. fragariae is between . The effect of pH is more difficult to understand; oospores germinate best in soils with a higher pH. In contrast, soils with a lower pH are better suited for the mycelium and more mature parts of the oomycete.
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Chlamydospores produce mycelium that continues to infect the plant. Pythium ultimum P. ultimum requires moist conditions to germinate. When conditions are favorable, surviving oospores in the soil produce a sporangia and zoospores which facilitate infection via germ tube. From there, mycelium will grow throughout all plant tissues.
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These then asexually bud into conidium spores. These structures create the characteristic grayish-white down-like appearance of downy mildew. Unlike other oomycetes, or Peronosclerospora, P. philippinensis is not known to produce oospores. There is no known sexual stage of the life cycle for P. philippinensis.
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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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Peronospora valerianellae is a plant pathogen. It causes downy mildew on leaves of lamb's lettuce Valerianella locusta, which is widely grown as a salad plant in several European countries (for example France and Germany). It is transmitted by seed-borne oospores, and is controlled by fungicide sprays of the foliage.
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Peronosclerospora sorghi is a plant pathogen. It is the causal agent of sorghum downy mildew. The pathogen is a fungal-like protist in the oomycota, or water mold, class. Peronosclerospora sorghi infects susceptible plants though sexual oospores, which survive in the soil, and asexual sporangia which are disseminated by wind.
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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 antheridia will be apical to the oogonial wall. Sometimes there will be two antheridial cells on one stalk. The yellowish oospores average 15 µm in diameter, have thick (~2 µm) walls, and are plerotic (fill the whole oogonium). Conidia are spherical at 8.8-30.8 μm diameter, but rarely produced.
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Secondary lesions appear after about 10 days, allowing the fungus to sporulate once more. This cycle can occur many times during one season, making Peronospora manshurica’s disease cycle is polycyclic. About 20 days after inoculation, oospores are formed within infected plant tissues. Like other oomycetes, this is accomplished by the fertilization of oogonia by antheridia.
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Phytophthora pluvialis is homothallic; it forms oogonia in culture. Its oogonia are terminal, smooth and globose, being approximately 30 µm in diameter, and possess amphigynous antheridia. Its oospores are globose and aplerotic, being about 28 µm in diameter. Sporangia formed in water are ovoid and slightly irregular, semi-papillate, terminal or subterminal, and partially caducous with medium-sized pedicels.
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Effect of Wind on the Dispersal of Oospores of Peronosclerospora sorghi from sorghum. Plant Pathology (1997) 46, 439-449. As the pathogen continues to develop in the host plant, there may also be production of conidia on the leaf surface. It is the conidia and the conidiophores that cause the white, downy growth on the undersides of the leaves.
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If the sorghum plants are older, the pathogen will often produce oospores in the leaves. Plants are usually capable of surviving this type of infection and will survive until maturity. The disease may cause the tassels and ears of maize plants to develop improperly or not form at all. This also occurs within the panicle of the sorghum plant.
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This continuous reproduction renders the plant dead at the end of the season. The oospores are then left to overwinter in the dead plant’s debris and the soil. The cycle is repeated once again in the spring when environmental conditions are favorable (see § Environment). The disease is mostly localized where zoospores initially infected the host plant.
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Beet leaves are less affected, so a crop can to a substantial effect recover from an attack on seedlings. Control relies on adequate crop rotation and avoidance of sources of infection (e.g. adequate control of the disease on beet seed crops), as oospores survive only 2–3 years in the soil. Individual infected plants may also be removed.
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Peronospora manshurica infects soybeans, reducing photosynthetic activity, yield, and quality. The fungus spreads by oospores on diseased leaves and/or on infected seed. The disease spreads in environments with high humidity and favors temperatures between 20-22 °C. Tufts of grayish to pale-colored sporangiophores on the underside of leaves easily distinguish the infection from other foliar diseases.
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In sorghum, chlorosis of the seedlings is very common after infection. As the leaves get older, they can express white striping, which eventually leads to the necrosis of the white striped tissue. When the leaves die, they begin to become shredded in appearance, similar to hail damage. This symptom is associated with the production of oospores in the leaf tissue.
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Homothallic reproduction is characterized by the fusion of the asexual oogonium and antheridium. This fusion leads to the formation and release of sexual oospores, the primary inoculum for the next season. Heterothallic sexual reproduction is the fusion of sexual cells from two separate organisms, leading to "outcrossing".Spring, O. (2000) Homothallic sexual reproduction in Plasmopara halstedii, the downy mildew of sunflower.
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Pythium survives over winter as oospores found in the soil. The pathogen therefore is easily spread with the movement of diseased plants, soil movement, surface water, or even from shoes. Pythium also causes "Damping off", "seed decay", or "seedling blight" of turfgrasses. This is most common in Perennial ryegrass (Lolium perenne) and happens in areas that are high above the recommended seeding rates.
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As with all fungicides, Metalaxyl is effective for prevention only and should be applied before the disease has established itself inside the tissues of the soybean plant. Replanting must be done once severe pre-emergence damping off is observed. Improving field drainage and soil tillage are cultural practices that can help minimize the effect of Phytophthora sojae. Improving soil tillage can help eliminate oospores from the soil.
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Plasmopara halstedii is a plant pathogenic oomycete, capable of overwintering in soil due to survival structures called oospores. For this reason, P. halstedii is a soil borne pathogen infecting the roots of the host plant.Ioos, R., Laugustin, L., Rose, S., Tourvieille, J. and de Labrouhe, D.T. (2007) Development of a PCR test to detect the downy mildew causal agent Plasmopara halstedii in sunflower seeds. Plant Pathol.
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The pathogen persists as mycelium systemically infecting onion bulbs, but is not known to be transmitted in onion seed. The pathogen can persist in the soil for several years as oospores. Systemically infected plants are dwarfed and pale green. Under moist conditions, the pathogen sporulates on the affected tissues and spreads to other plants, on the leaves and stalks of which it forms greyish-violet local lesions.
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Other Colocasia plants such as Elephant-ear and Dasheen are an additional means of survival for this pathogen. Finally, chlamydospores have been produced under ideal laboratory conditions in culture, and may also serve as a survival structure in addition to oospores. However, chlamydospores have not yet been observed in the field. Therefore, it is not known if chlamydospores are really part of the Phytophthora colocasiae disease cycle.
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Motile male gametes will exit the antheridia and are chemotactically attracted to oogonia. A single sperm cell will pass through a pore opening in the oogonial cell wall, allowing fertilization. Zygotes (oospores) are initially green but will gradually become an orange-red colour and develop a thick multilayered cell wall with species specific surface adornments. Meiosis occurs in the zygote prior to germination, producing four multi-flagellated cells after germination.
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293x293pxThe asexual life cycle of Phytophthora infestans is characterized by alternating phases of hyphal growth, sporulation, sporangia germination (either through zoospore release or direct germination, i.e. germ tube emergence from the sporangium), and the re-establishment of hyphal growth. There is also a sexual cycle, which occurs when isolates of opposite mating type (A1 and A2) meet. Hormonal communication triggers the formation of the sexual spores, called oospores.
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The zoospores released from sporangia are biflagellated and chemotactic, allowing further movement of P. infestans on water films found on leaves or soils. Both sporangia and zoospores are short-lived, in contrast to oospores which can persist in a viable form for many years. The color of potato sign is white. People can observe Phytophthora infestans produce sporangia and sporangiophores on the surface of potato stems and leaves.
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Zoospores - Reproductive Structure of the Phytophthora Buckeye rot of tomato is soil-borne and therefore affects fruit lying on, or close to, the soil. The fungi are spread by surface water, spattering rain, and furrow irrigation. While it can sexually reproduce through the production of oospores, its primary form of reproduction is by asexually producing sporangia. These sporangia are found at the tips of sporangiophores that emerge through the stomates.
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It will only grow in the 15-35 °C range. Mild winters correlate with higher infestations and lower crop yields, possibly due to decreased temperatures inducing the development of sex organs in the oomycete. Losses can be combated by destroying diseased fronds and exposing thalli to the air for 3–4 hours daily. The oospores can be spread in contaminated organic matter and the sporangia can spread through the water.
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P. hydropathica is a heterothallic oomycete, meaning that both mating types need to be present in order to sexually reproduce . The A1 mating type has been reported to be highly represented in populations . The species produce plerotic oospores and round antheridia, with observations of the sexual bodies being golden in color . Nonpapillate and noncaducous sporangia are produced, with varying shapes (obpyriform, ovoid, and nearly spherical), and are able to release zoospores.
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Plant pathologists Ross Beever and Nick Waipara recognised this as a distinct Phytophthora species and it was named Phytophthora 'taxon Agathis' (abbreviated PTA). It was formally named Phytophthora agathidicida in 2015. Phytophthora agathidicida is a species in the group of Phytophthora called ‘Clade 5’ which is defined by ITS DNA sequences. Within Clade 5 P. agathidicida can be distinguished from the other species by DNA sequence differences and oospores that have a moderately bumpy surface.
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It is most serious on the flowerhead types (cauliflower, broccoli), less serious on the leaf brassicas (cabbage, Brussels sprouts, and least serious on the root brassicas (turnips, swedes) and oil brassicas (rape). The pathogen persists as oospores in the soil. Attacks are most important in Brassica seedbeds, with infection appearing as yellow speckling of the upper surface of seedling leaves, and white mildew on the lower surface. Severely affected seedlings are stunted or killed.
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The exceptions involve oospores, and hyphae present within tubers. The persistence of viable pathogen within tubers, such as those that are left in the ground after the previous year's harvest or left in cull piles is a major problem in disease management. In particular, volunteer plants sprouting from infected tubers are thought to be a major source of inoculum at the start of a growing season. This can have devastating effects by destroying entire crops.
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These motile spores will move on to infect a root in the soil. Throughout the season if conditions are warm and wet enough the sporangium will continue to make more zoospores which can go no to infect other roots. It is within an infected root that additional oospores will be produced to overwinter another season. Although disease develops in less heavy soils, a heavy textured soil is favorable as they tend to remain wetter.
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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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Due to the infection, the stele of the root turns a wine to brick red, and starts to decay and die from the tip upwards. Red color of the roots does not necessarily guarantee the presence of P. fragariae infection. The most dependable way to determine if a plant has P. fragariae is the presence of microscopic oospores. Another symptom of P. fragariae is badly rooted lateral roots, starting to turn a grey or brown color.
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Papaver somniferum is susceptible to several fungal, insect and virus infections including seed borne diseases such as downy mildew and root rot. The use of pesticides in combination to cultural methods have been considered as major control measures for various poppy diseases. The fungal pathogen Peronospora arborescensis, the causal agent of downy mildew, occurs preferentially during wet and humid conditions. This oomycete penetrates the roots through oospores and infects the leaves as conidia in a secondary infection.
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The pathogen thrives under cool and moist conditions, but can do well under a wide range of conditions. Optimum conditions for sporulation are 59 °F (15 °C) with 6 to 12 hours of moisture present, often in the form of morning dew. Even when high daytime temperatures are not favorable for the pathogen (>95 °F or >35 °C), nighttime temperatures may be very suitable. Oospores (thick-walled, resting spores) of P. cubensis are rare and their role in nature is unknown.
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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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Spizellomycetalean chytrids have beneficial roles in the soil for nutrient recycling and as parasites of organisms that attack plants, such as nematodes and oospores of downy mildews. On the other hand, they also have detrimental roles as parasites of arbuscular mycorrhizae, symbiotic fungi that help plants gain essential nutrients. Culture isolation studies and molecular characterization of these fungi have demonstrated a great deal of undescribed diversity within the Spizellomycetales, even for isolates collected within the same geographic location. Thus, these understudied fungi await greater exploration.
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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.
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As an extra precautionary measure, a grower can choose to have their soil either heat- sterilized or pasteurized. This process heats the soil to very high temperatures, with intentions to destroy the overwintering oospores which would otherwise restart the disease cycle in the spring. This practice of soil sterilization can be very costly, and may not complete eradicate all of the resting spores. However, if the problem is extreme enough, it may be one of the last options left, asides from finding a new plot of land.
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P. megakarya is an oomycete that has a polycyclic disease cycle, producing three asexual spore types: sporangia, zoospores, and chlamydospores. Although it is rare, P. megakarya can also produce sexual oospores through heterothallic mating which requires two different mating types; so far none have been observed. Mycelium plays an important role in the infection of the cocoa trees; mycelium found in the soil and in cankers on the bark develops into sporangia, which can then germinate. Zoospores are produced from these sporangia as secondary inoculum.
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Upon infection, oospores that overwinter on leaf tissue and petioles give rise to sporangiophores which have lemon-shaped sporangia at their tips. Sporangia can infect taro leaves either directly via germ tubes or indirectly by producing zoospores. Whether sporangia infect directly or indirectly depends on weather conditions. If weather conditions are favorable, such as warm temperatures, sporangia infect directly via germ tubes. Germ tubes give rise to appressorium which form haustorium and allow the pathogen to extract nutrients without penetrating the host’s cell membrane.
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The second plant agent in the model is Chara aspera, also a rooted aquatic plant. One major difference in the two plants is that the latter reproduces through the use of very small seeds called oospores and bulbills which are spread via the flow of water. Chara aspera only grows up to 20 cm and requires very good light conditions as well as good water quality, all of which are limiting factors on the growth of the plant. Chara aspera has a higher growth rate than Potamogeton pectinatus but has a much shorter life span.
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Physiological and Molecular Plant Pathology 40:17-22 Once zoospores have made contact with the host root, they encyst on the surface, break down the plant cell wall with proteolytic enzymes and begin to germinate. Their hyphae will begin to grow through the intercellular space of the plant cells. After establishing its haustoria for nutrients, more oospores will begin to form in the cortical cells of the root. The host plant will begin to exhibit secondary symptoms such as stem canker, wilting, and chlorosis as Phytophthora sojae continue to reproduce.
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Unlike most species of Phytophthora, which are diploid, P. alni alni is near tetraploid and unable to complete meiosis beyond metaphase I. In culture, many oogonia prematurely abort or appear abnormal and only one third of the oospores that appear normal are reported to be viable. As a result, it is believed to spread predominantly via asexual means, namely zoospores which are produced in a specialised structure known as the sporangium. Water temperature has been shown to affect sporulation, with warmer water increasing sporangia production. Temperatures of 8 °C and below prevent production of sporangia.
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In the spring the oospores germinate and produce sporangia on short stalks called sporangiophores that become so tightly packed within the leaf that they rupture the epidermis and are consequently spread by the wind. The liberated sporangia in turn can either germinate directly with a germ tube or begin to produce biflagellate motile zoospores. These zoospores then swim in a film of water to a suitable site and each one produces a germ tube - like that of the sporangium - that penetrates the stoma. When the oomycete has successfully invaded the host plant, it grows and continues to reproduce.
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Hyaloperonospora differs from Perofascia in that its sporangiophores are tree-like, its haustoria are lobate to globose, and the walls of its oospores are relatively thinner. The life history does not differ from that of Peronospora, the genus that Hyaloperonospora species used to be classified under. It begins as sporangia, which are small spore-like structure, and when it lands next to a leaf stoma, it germinates a germ-tube. The germ tube enters the leaf cell creating a haustorium, which allows the mould the uptake nutrients from the leaf. The mould will continue to grow, with hyphae extending into the leaf’s intercellular space.
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