How does direct transmission of plant diseases occur?

Direct transmission of plant diseases occurs through direct contact of a healthy plant with any part of an infected plant.

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How are plant diseases transmitted via soil contamination?

Plant diseases are transmitted when infected plants leave pathogens or spores in the soil, ready to infect other plants.

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What are some examples of vectors that transmit pathogens between plants?

  1. Wind
  2. Water
  3. Animals
  4. Humans

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How can humans transmit plant pathogens and spores?

Humans transmit plant pathogens and spores by handling plants, clothing and farming tools, as well as through farming practices.

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How does over-crowding affect the risk of plant diseases?

Over-crowding increases the risk of plant disease as plants are more likely to be in direct contact. 

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How does poor mineral nutrition affect the risk of plant diseases?

Poor mineral nutrition reduces the resistance of plants.

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Give an example of a plant disease that is caused by each of the following: a bacterium, a virus, a fungus and a protoctist.

  1. Ring rot is caused by a bacterium.
  2. Tobacco mosaic virus is caused by a virus. 
  3. Black sigtoka is caused by a fungus. 
  4. Potato blight is caused by a protoctist.

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What are some physical defence mechanisms plants have against pathogens?

  1. Waxy cuticles
  2. Cell walls
  3. Production of callose

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What are the functions of waxy cuticles and cell walls in plant defence?

They provide a physical barrier against pathogens.

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What is callose and how does it contribute to plant defence?

Callose is a polysaccharide deposited between the cell wall and plasma membrane to make it harder for pathogens to enter cells.

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What chemicals do plants produce to defend themselves against pathogens?

  1. Insect repellents
  2. Insecticides
  3. Antibacterial substances
  4. Toxins 

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Why do plants produce insect repellents and insecticides? 

Plants produce insect repellents and insecticides to prevent insects from transmitting pathogens. 

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Why do plants produce antibacterial substances?

Plants produce antibacterial substances to kill bacteria or inhibit their growth. 

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