Phytophthora

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Dr. Harisingh gour central university sagar
(M.P.)
General characteristics and life cycle of
Oomycetes.
Phytophthora
Submitted to- Dr. Yogesh Bhargav, (Department of
applied microbiology).
Submitted by - Priyanshi mishra, Msc Ist
Semester.
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Oomycetes

• Cellulose walled fungi.
• Consist of Four orders-
• Saprolegniales (freshwater saprotrophs, eg.
  Achlya, saprolegnia).
• Leptomitales (Fermentative aquatic fungi),
• Lagenidales (plant root parasites),
• Perenosporales (plant pathogens).
• Contain 74 genera with 580 species.
• Aquatic,
• Mode of nutrition Free living (Saprophytic) or
  parasitic.
• Habitat most members are aquatic but some grow
  on soil and other attack shoot of terrestrial
  plants.
• Primitive forms are unicellular, advanced forms
  are branched, filamentous and coenocytic
  mycelium.
• Cell wall composed of cellulose-beta-glucan and
  chitin is altogether absent.
• Asexual reproduction takes place by pyriform and
  reniform.
• Sexual reproduction is oogamous type.
• Many members helps to understand evolutionary
  migration of fungi from aquatic to terrestrial.
• Causes plant diseases.

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Phytophthora
Greek phyton plant, Thora destruction. (Plant
destroyer)

• Genus first described by Heinrich Anton de bary
  in 1875.
• Genus is cosmopolitan.
• Wider host range.
• Eg. P. Cactorum recorded over 200 species and
  60 families of flowering plants
• p. Cinnamon 1000 plants causes several
  disease especially on woody hosts.
• Phytophthora are pathogenic to dicotylednous
  crop.
• Differ merely in extent to which they have free
  living saprotrophic phase.
• May survive in soil atleast in the form of
  oospores, or in infected host tissue.
• All Pathogenic forms isolated from host and can
  be grown in pure culture.
• Selective media, often incorporating antibiotics
  or fungicide such as pimaricin or benomyl, have
  been devised for isolation of phytophthora.
• Most destructive in low temperature and high
  humidity.

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General characteristics

• Facultative parasites,
• Eucarpic thallus,
• Mycelium is well developed, filamentous branched
  (right angle),Coenocytic (aseptate), healing,
  intercellular with haustoria Mycelium.
• Cell wall primarily composed of cellulose.

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Classification

• Kingdom mycota,
• Phylum oomyceta,
• Class oomycetes,
• Order Perosporales,
• Family phythiaceae,
• Genus phytophthora,
• Species infestans,
• colocasiae,
• Parasitica.

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Vegetative structure

• Mycelium is coenocytic aseptate, healing and
  monopodial branching.
• Septa formed at the time of reproduction or at
  maturity.
• The cell wall consist of glucan, chitin is
  however absent.
• Cytoplasm contains many nuclei, mitochondria,
  endoplasmic reticulum, ribosome, dictyosomes,
  vacuoles and many oil globules.
• The mycelium is intracellular and directly kills
  invaded cells. In some cases it is intercellular.
• Haustoria developes as lateral outgrowth from the
  intercellular hyphae.
• Cytoplasm of haustoria contains mitochondria,
  ribosome, endoplasmic reticulum and nuclei.

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Life cycle
Three mechanism of life cycle
Vegetative reproduction
Asexual reproduction
Sexual Reproduction
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Vegetative reproduction

• Many species of pythophthora (P.colocasiae and P.
  Parasitica) reproduce by chlamydospores.
• Chlamydospores may be terminal or internally.
• They germinate by giving rise to 3-11 germ tubes
  which generally develop sporangia at their tip.

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Asexual cycle
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Cont
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Sexual cycle
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Graphical life cycle
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Disease caused

• Most species of phytophthora are soil borne plant
  pathogens causing disease of both herbaceous and
  woody mostly dicotylednous plant. Example Root
  rot, basal stem rot, leaf spot or blight as well
  as fruit rot.

• Phytophthora citricola Root rot and stem cancers
  in citrus trees,
• Phytophthora fregariae Red root rot affecting
  strawberries,
• Phytophthora infestans potato late blight
• Phytophthora palmivora Fruit rot of coconut and
  betel nuts,
• Phytophthora ramorum sudden oak death,
• Phytophthora sajae soybean root rot,
• Phytophthora colocasiae colocasia blight ,
• Phytophthora nicotianae Black shank disease of
  tobacco,
• Phytophthora cactorum bud rot of coconut,
• Phytophthora arecae seedling blight of areca
  nuts,
• Phytophthora erythrosepica pink rot of potato.

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Symptoms of disease caused by phytophthora

• The disease appears as small black or purplish
  black areas at margins and tip of leaf.
• These patches gradually enlarge under favorable
  conditions. All part of host undergo browning and
  rotting.
• If the soil is very moist, tubers are also
  affected and may rot completely.
• In colocasia, large, circular, ovular irregular
  yellowish brown areas appear on leaves. Drops of
  a yellow liquid oozes out from the leaf surface,
  rotten of corms results in severe infection.

Control of phytophthora

• Cultivation of resistant varieties.
• Spraying of fungicide like Bordeaux mixture.
• Destruction of infected foliage by Spraying with
  sulphuric acid, copper sulphuric, dithane and
  Fytolan.
• Seed tubers should be obtained from areas where
  disease does not occur.
• Tubers should be covered with a thick layer of
  soil. It will avoid the chances of spores coming
  in contact with them.
• Good drainage system should be maintained.

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