UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 21/05/2023 [SEARCH]

Plant disease: 5. The control, reduction and prevention of plant diseases

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(5) The control, reduction and prevention of plant diseases

Aphids have already been mentioned in the introduction!

Plants are the start of most food chains, so they are of obvious importance to any subsequent source of food.

Plant crops are the most important source of food for most of the World's population.

In poorer and developing countries anything that reduces crop yields affects people and can lead to famine.

The causes are usually the weather, increasingly so by climate change and disease affected plants.

Plant disease can also affect:

ecosystems, affecting the balance of populations,

biodiversity, some plant species might be more susceptible to pathogen attack than others, possibly removing a whole local population of a plant species.

Therefore, it is obviously important to control plant disease as much as we are able to, but with little if any environmental costs!

The first step would be to identify the disease-pathogen affecting the plants (described in the next section).

Examples of methods of controlling plant disease

Destroying affected plants:

This removes the source of infection, BUT, wasted crops are costly to the farmer.

Healthy plants to start with

By using healthy plants, free of infection, you avoid introducing a plant disease to wherever you plant them.

Chemical control:

Fungicide sprays can be used to kill fungal infections. Bulbs and seeds can be coated with an anti-fungal agent that prevents the attack of the pathogen in the first place.

BUT, evolution is always at work, throwing up mutations in the DNA of the pathogens. The result is the formation of pathogen strains which are resistant to the chemical.

Biological control:

Crown gall disease can be prevented by dipping the roots of the plant into a suspension of a similar bacterium.

This is done before the plant is planted in a potentially infected soil.

The selected bacteria does not infect the plant, but it does produce an antibiotic that prevents the crown gall pathogen from reproducing.

You can use another organism to control an insect pest of viral/bacterial pathogen e.g. predatory insects.

Ladybirds are very fond of the aphid insect, so ladybirds can be released to reduce the population of aphids.

This is fine as long as the introduced controlling organism doesn't become a pest itself, causing further problems!

Crop rotation:

Since many pathogens are specific to a particular plant, changing the plant that grows in a particular field inhibits the pathogen from becoming permanently established in that location.

However, there is an economic consequence of crop rotation - extra cost from having to change crop each year.

Controlling the movement of plant material:

The basic idea is to prevent diseased plants from coming into contact with healthy plants and slow down the spread of the disease e.g.

To slow down Chalara ash dieback disease you can remove infected ash trees and replanting them with other different tree species e.g. birch

Plant nurseries must be careful not to sell infected plants and must adhere to any sale restriction regulations e.g. the import and export of plants such as ash trees or any other potentially disease carrying plant.

Polyculture methods of crop production

Polyculture involves growing different types of plants in alternately within the same single area at the same time.

The idea is that if a pathogen is present and specific to a particular plant species, it is less likely to infect neighbouring plants of a different species.

Thus limiting the spread of the pathogen through the crop.

Genetically modified plants for agriculture (the controversial GM crops)

Plant scientists are working on the development of disease-resistant crops by gene modification.

One particular problem are fungal rusts that cause decreased crop yields in things like apples, coffee, oats and pears, amongst many other types of crop.

It is hoped that GM plant seed will maintain or even increase crop yields.

Disease resistant crops can be cloned and plant cells and plants can be made in large numbers quickly.

See methods of cloning plants for more details


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