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GCSE level School biology revision notes: How to produce new varieties of plants

GCSE level Biology exam revision notes on variation in plants

How do we produce new varieties of flowering plants? including traditional breeding techniques - selection for useful or other desired characteristics

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[Key points and learning objectives for this page, after the main body of notes]

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Questions to be answered: How do we produce new varieties of plants? Why do we need new varieties of plants?  Why is genetic variation in plant species a good thing?

(a) Introduction - why genetic variation matters

(b) Traditional plant breeding methodology

(c) What it takes to produce a new variety

(a) Introduction - why natural genetic variation matters

Any population of an organism which lacks variety in its gene pool is particularly susceptible to various factors.

This is the case

e.g. climate change - change in weather patterns

attack by a pathogen - bacteria, fungus or virus

If any of one these factors affect a population, in a varied gene pool, not all of the population will die.

Those individuals with the right set of genes will survive.

The survivors will be able to reproduce and pass on the advantageous genes.

These days new crop varieties in agriculture are bred for disease resistance - lost or poor crop yields costs money!

Increased yields of better quality food crops is a worthy economic goal.

Horticulturalists - plant breeders, are also interested in quality flowers, fruit or vegetables for garden cultivation.

The 'ideal aims' for crops i.e. beneficial characteristics of the variety are:

Plants that grow and mature quickly with good crop yields.

Crops that have a long shelf-life and store well (e.g. flowers), or can be frozen (e.g. vegetables.

Vegetables that have a distinctive taste, looks and texture.

Flowers that are attractive to look at e.g. in colour,  have a pleasing aroma-scent, perhaps larger and bigger than their wild origins!

However, its a good idea to preserve wild versions of plants we cultivate and use their wide-ranging gene pool for future breeding programmes.

In order to achieve these aims you need to:

Selectively breed a variety in large numbers of identical plants to give the greatest possibility of being able to select the plants with desired characteristics i.e. those listed above.

BUT, there is the danger of having crops that are genetically too uniform - as already discussed (at the start), a narrow gene pool is susceptible various things.

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(b) Traditional plant breeding methodology

In traditional plant breeding, a plant with desirable characteristics is crossed with another plant with the same or another desirable characteristic.

The plants are chosen from a mixed population or existing varieties.

Pollen is transferred from the flowers of one plant to the flowers of another to fertilise it - you can just dust off the pollen from the anther of one flower with a fine paint brush and dab the pollen onto the stigma of another flower.

To ensure the desired breeding direction - that is to concentrate the gene pool of desired traits, you must stop the plants from self-pollinating each other and also avoid cross-pollinating with a different plant variety.

From the new plant seeds the process is repeated over several generations until an acceptable new variety is created.

For more see reproduction in flowering plants

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(c) What it takes to produce a new variety by traditional breeding methods

Quite a lot as it happens!  Especially if you want to combine several desirable traits in the same plant e.g.

(i) You might want a crop of grain or vegetables to give an increased yield and be disease resistant.

(ii) You might want a flower to be large, attractive in colour and a beautiful scent.

Unfortunately, a plant breeding process is very expensive and might take many years to develop the 'product'

It involves lots of selection of plants to cross-breed and lot of 'trial and error' as the results are uncertain!

 

The basic sequence to develop a new variety of a plant species is outlined below 

(its a sort of 'algorithm!)

Sequence Stage in breeding programme Comments on each step
1 A male flower is fertilised with pollen You must prevent self-fertilising or cross-pollination with another plant
2 Seeds collected and the plants grown You need thousands of individual plants to provide as wider gene pool as possible
3a The plants are exposed to whatever you want the plant to be tolerant of e.g. to have disease resistance The plants are tested for exposure to a disease induced by a bacteria, fungus or a virus
3b OR maybe measuring the size and colour of a flower, or it might be the yield of a fruit Plants examined for quality of flower or yield of fruit
4a Select plants from stage 3a, looking closely at the characteristics e.g. signs of disease resistance etc. You are the picking the plants that seem to show most disease resistance
4b Select plants from stage 3b, monitoring the colour of the flower or the yield of fruit You are the picking the plants that seem the 'best' colour' or the 'best' yield
5 Repeat breeding from the stage 4 selection - picking those plants closest to the desired traits  You keep on repeating the sequence and hope it works out to provide a healthy breeding line
6 Finally, you have a breeding line of plants with the desired characteristics - a new variety is born! BUT, you are dealing with a narrowed gene pool.

Key points on producing new varieties of plants

Source of information is based on textbooks and syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10)

Revision notes for biology students on how new plant varieties are produced, with a focus on traditional selective breeding techniques:

Producing New Varieties of Plants

Creating new plant varieties involves selecting and breeding plants that show useful characteristics - such as disease resistance, higher yield, or drought tolerance - by using genetic variation already present in a population.

1. Genetic Variation: The Foundation

  • Variation exists naturally within plant species due to:
    • Mutations
    • Meiosis during sexual reproduction
    • Cross-pollination between genetically different plants
  • Some traits are inherited and controlled by genes, such as:
    • Colour of fruits/flowers
    • Growth rate
    • Resistance to pests or drought

2. Traditional Selective Breeding (Artificial Selection)

This method has been used by farmers and horticulturists for centuries.

Step-by-Step Process:

  1. Choose parent plants with desirable traits
    (e.g. high fruit yield, disease resistance)
  2. Cross-pollinate selected parents
    (or allow natural pollination and manually select successful offspring)
  3. Grow seeds from offspring (F1 generation)
  4. Select the best offspring that show the desired traits
  5. Repeat the process over multiple generations to reinforce the traits

Examples of Desirable Traits Selected For:

  • Pest or disease resistance
  • Drought tolerance
  • Faster growth or larger leaves
  • Improved taste, colour, or shelf life
  • Higher crop yield

Advantages of Traditional Breeding

  • Simple and inexpensive
  • Uses naturally occurring variation
  • Accepted by most consumers (non-GM)

Disadvantages

  • Time-consuming (multiple generations required)
  • May unintentionally select harmful traits
  • Genetic diversity may decrease if few plants are used

Summary Table

Feature Details
Source of variation Natural genetic differences within a species
Key method Selective breeding (choosing parents with desired traits)
Time required Several generations
End result A new variety with specific, useful features

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