Fungal diseases in plants

RUSTS

Causative agent: Puccinia graminh (Basidiomycota) Affected plants: Wheat, barberry Symptoms:

  1. Reddish streaks (pustules) appear on the stems and other parts of wheat. These streaks may affect most of the plant. They give rusted appearance to whole of the plant.
  2. As the season advance-, the streaks change from red to bl wk. The crop gives burnt dried look.
  3. The barberry plant shows the presence of small circular yellow

s jots on the tipper surface of leaves. They are changed into flask-shaped pycnidia. Pycnidia contain hyphae and pycnichospores. The leaf bears cup-like structures on the ventral surface. These are called cluster-cups or aecidia. Aecidia contain aecidiospores.

Host parasite relationship: Uredospores and aecidiospores genninate on wheat. They produce germ-tubes. Germ lute enters thro ‘eh the stomata. It develops into intercellular mycelium. This mycelium develops haustoria.

Environmental Relationship: Moderate temperature and abundant rainfall favours this disease.

Disease cycle: Puccinia graminis is heterocious rust. Its life cycle is comnleted in two hosts, wheat and barberry. It produces five distinct spores from spring to autumn. These spores are basid:ospores pycnidiospores, aecidiospores, uredospores and teleutospores. They are very different type of spores. Each spore has a distinct function.

I. Uredospores: The uredospores function as asexual spor:s. They are dispersed by wind. They spread infection from one plant to ete other. The uredospores and teleutospores cause red a id black soots on wheat.

  1. Teleutospores: The teleutospores are final spores on wheat. They fall down on the soil and remain dormant till spring.
  2. Dasidiospores: Teleutospores germinate in next spring to produce basidiospores. The basidiospore germinates only on barberry leaf.
  3. Pycnidiospores: Pycnidia arise on barberry plant. Pycnidiaproduce pycnidiospores. The pycnidiospores are involved in farti I ization.5. Aecidiospores: Pycnidiospores produces aecidia in barberry. Aecidia produce aecidiospores. The aecidiospores re-infect the vateat. It completes the life cycle.

    Control measures

    I. Destroy the alternate host the barberry plants.

    2. Use of resistant varieties.

    3. Proper drainage of the soil.

    4. Avoid excess use of nitrogenous manures. It promotes growth of r .1st-fungus.

    SMUT (Wheat, oat, barley)

    Causative Agents: Usiilago Odd, U. avenue and U. nuda (Class Basidiomycota)

    Affccted plants: Wheat. oat. barrel,

    Hosl-parasite Relationship: Two Thyphae tbse to form dikaryotic inycdium. The mycelium sends haustoria in host-tissue to absorb fooc.

    Environmental Relationship: Cool and humid weather at flowering time is favourable.

    Syn: ptoms: The plants are infected at an early stage. But the fungus appears at the flowering stage. The ears become black. The. grains are ..eplaced by loose dark-brown or sooty powder. This powder is composed of chlamydospores. The powder is easily blown away. The grains are totally destroyed.

    Distase cycle: The infection takes place at any time during the flmsering period of the host. Infection is occurred by different ways:

    1. By chlamydospores: The dikaryotie secondary mycelium spreads in the host. It produces chlamydospores. Thlamydospores fall on the stigma ot flower. They germinate • here and send infection-threads into the ovary. They remain Jormant there. When such seeds are sown, the fungus become active and infects the whole plant.
    2. By basidiospores and conidia: Some chlanaydospores fall on he ground. They germinate in the soil and produce basidiospores and conidia by budding. Basidiospores and conidia by budding.Basidiospores and conidia are spread by wind and cause infection in the stem.
    3. Control Measures:Following measures should be taken to control this disease:
      1. The seed grains should be treated with organomercury disinfectants before sowing.
      2. -lot water treatment should be given to the seeds. The grains should be sub-merged for 10 minutes in water at a temperature vtween 52°C and 54°C. The temperature should be kept within these narrow limits. Below 52°C the fungus is no: killed. Whereas above 54°C the embryo of the seed is injured.
      3. Sun treatment: This is a modification of the above method. This s practiced where the summer temperature is very high. The suspected seeds are soaked in water and exposed to thc heat of he summer sun for 4 hours (from 8A.M. to 12 noon).
      4. Copper dust and sulphur dust should be sprayed on plant
      5. Grow the resistant varieties of wheat and other plants.

      Downy mildew (Grapes, Bajra)

      Causative agent: Plasmophara vilicola (Grapes)„Meracporci graninicola (Bajra)

      AlTicted plants: Grapes and Bajra

      Syn. ptoms: The early symptom of the disease is the appearance of sma.I greenish yellow oily spots on the dorsal surface of tin leaves. The spots gradually increase in size. They fuse and become brown. The sporangiophores of downy mildew appear on the !owe; surface of ti e leaves. The infected leaves dry up. They become brittle and fall AT. The disease spreads to other parts of the plant. The berries shou brown patches with downy growth. Their colour turns to grayish brown or dark-brown.

      Environmental Relationship: Moist weather is suitable for the attack of this disease. But this disease disappears in dry hot weather. Hos ...parasite Relationship: Downy mildew is an obligate parasite. Its mycelium is intercellular. It sends haustoria into the host cells. Disease cycle: The fungus survives as oospore in the dead plant. Or its mycelium survives in the perennial hosts. The sporangiophore coin :s out through stomata. The sporangia produce zoospores. Zoospore dispersed by wind. The zoospores enter through the storr ata.

      Control measures: Bordeaux mixture should be sprayed on the plan for controlling this disease.

      Powdery mildew (Grapes, Barely, wheat)

      Causal agent: Uncinula necator (Grapes), Etysiphe graminis (wheat barely)

      Symptoms: This diseases cause malformation and discoloration of leaves. It forms whitish-grey patches on the upper or under surface. The affected parts of the stem are at first whitish-grey. But later they turn dark brown. The berries or grains become irregular in dmpe. It is reduced in size and develops cracks. The plant shows dwarfed appearance.

      Host-parasite Relationship: The mycelium spreads over the host i.e., stern, leaves and fruits. The hyphae are attached by aspersoria. Aspmsoria sends haustoria into the epidermal cells of the host to abscrb food. The superficial mycelium gives the plains dusty powered appearance.

      Environmental Relationship: Wind, dry weather, low hum dity and cloudiness promote the disease.

      Dist ase-cycle: The disease is air-borne. The conidia and asimspores are carried by the wind to other hosts.

      Control measures: The plants should be dusted with fine sulphur at regular intervals to control this disease. All diseases plants should be dest tayed. Applications of copper containing spray also control this disease.

      Damping off disease (Tobacco)

      Causative Agent: Pythium de Baryanum, P. myriotylum.

      Affected plant: Tobacco

      Sym ptoms: Diseased plants turn pale-green. They show a girdle of brown colour near the surface of the soil in the region of hypocotyls. The:’ collapse due to the weakening of tissue at the base of the stem. Environmental Relationship: Disease spreads in poorly aerated and watt r-logged soils at high temperature.

      Disease cycle: The pathogen survives in the soil as oospore. Oospore germinates to produce zoospores. The zoospores attack fir:. young seedling. The host shows disease symptoms in the region of hypocotyl near the ground level.

      Control measures: Soil should be sterilized. Good drairage and proper aeration of the soil retard this disease. The seeds should be treated with copper carbonate, copper chloride and formalin.

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