From merosporangia and kidney or bean shaped

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from merosporangia) and kidney or bean- shaped secondary (second from first cyst formed). S/n Primary Zoospores Secondary Zoospores 1 flagella anteriorly inserted flagella posteriorly inserted 2 encyst by withdrawal of flagella Encyst by shedding Flagella 3 Swims for minutes Swims for hours 4 tuft of flagella that formed the tripartite tubular hairs in encysted state encysted zoospores shows boat hook hairs for attachment
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Continuation (iii) In some species, only secondary zoosporangium are produced with the primary once suppressed e.g. Dictychus . The zoospores after a period of swimming, they encyst in response to stress and germinate to release a secondary zoospore which swims, eventually germinates to form a thallus.
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Continuation During sexual reproduction, the somatic hypha matures and produce gametangia (antheridium and Oogonium). This is followed by gametic copulation leading to the fusion of egg nuclei of the oogonium and the sperm cells that travel through a tube. The fertilized oosphere forms the zygote which later organize into the oospore. The oospore germinates to also
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Fig. 16: Life Cycle of Saprolegnia parasitica
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Fig. 17: Variation in zoospore formation, release and habit
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Peronosporales
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Order - Peronosporales In habit, members of this order range from aquatic to amphibious to terrestrial way of life. Many species are parasite with a few living as saprophytes. Some of the parasitic species can also survive as saprobes following the death of their host. Sporangia is not elongated but rather globose or oval in shape and may function as detachable/deciduous, germinable conidia in some species. Reniform/kidney-shaped, monoplanetic zoospores are produce in the Peronosporales Oogonium structure is differentiated into inner ooplasm and outer periplasm. Sporangiophore is more distinct in the Peronosporales indicative of their higher evolutionary position compared to the Saprolegniales.
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Continuation Oogonium in the Peronosporales contains a single egg cell. The Order is distributed into 3 Families on the basis of their sporangia and sporangiophore (i)Pythiaceae – haustoria absent or branched, facultative parasites, sporangiophore undifferentiated from mycelium e.g. Pythium debaryanum . (ii)Peronosporaceae – sporangiophore distinct and branched, sporangia singly or in clusters, haustoria varied or branched e.g. Peronospora parasitica . (iii) Albuginaceae – sporangiophores unbranched, produce a chain of conidia in basipetal succession, haustoria is knob shaped e.g. Albugo candida
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Family - Pythiaceae Members of this Family cause serious disease of plants and animals. Produced varied shape of sporangia and few exhibit sporangial proliferation The Family include genera like Pythium and Phytophthora .
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  • Fall '19
  • Spore, Slime mold, multinucleate sporangia

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