Diagram showing difference between conventional and GM plant breeding

What is the difference between conventional and GM plant breeding?

Both conventional and genetically modified plant breeding change the genes of a plant so that a new and better variety is developed, but what makes them different? Find out in this fact sheet.

  • 8 November 2007 | Updated 14 October 2011

Conventional plant breeding

Conventional plant breeding involves changing the genes of a plant so that a new and better variety is developed. New varieties of plants are bred to suit different climate conditions, improve taste or nutritional value, cope with disease or pests better, or to use water or nutrients more efficiently for example.

To conventionally breed a new plant variety two closely related plants are ‘sexually crossed’. The aim is to combine the favourable traits from both parent plants and exclude their unwanted traits in a singular new and better plant variety.

However, the progeny of this first cross inherit a mix of genes from both parent plants and so both positive and negative traits may be inherited.

Breeders have to look at all the progeny and select the ones with the most positive traits and least negative traits. They then cross this selected progeny back to one of the original parent plants to try and transfer more of its positive traits into the following generation.
This process called ‘back-crossing’ takes place over a number of generations, which usually means a number of years, until the progeny have all the desirable traits and none of the negative ones of the original two parent plants.

For example, a wheat variety that produces high yields in a one region may be susceptible to a new disease. Another wheat plant may have very low yield, but has resistance to the new disease. Breeders can cross and backcross these two parent wheat varieties and their progeny with the aim of combining the high yielding qualities from that parent with the disease resistance from the other parent.

Conventional plant breeding may also use ‘wider crosses’ that involve crossing species or even genera that are quite unrelated. These crosses cannot occur without help – so sophisticated techniques are employed.

Genetic modification (GM) plant breeding

Breeding using genetic modification (GM) also involves changing the genes of a plant so that a new and better variety is developed. It is done for the same reasons as conventional breeding. The key difference is that instead of randomly mixing genes, which occurs as a result of a sexual cross, a specific gene, which is associated with a desirable trait, is selected and inserted directly into the new plant variety.

  Diagram showing difference between conventional and GM plant breeding
 The difference between GM and conventional plant breeding. Click for larger image.

This can save time and reduces the chance of undesirable traits in the new plant variety.

GM also allows breeders to use genes from unrelated plants and sometimes other organisms into a new variety. This means breeders can access and use a wider choice of genetic diversity to develop new plant varieties. This is possible because all genetic information is stored in DNA – which is the same chemical in all organisms.

In Australia, GM insect-resistant cotton contains genes from a soil bacterium, Bacillus thuringiensis (Bt), that provide very specific protection for the cotton against cotton’s number one pest – Helicoverpa caterpillars. Across cotton’s entire genetic diversity it does not have any genes that give Helicoverpa resistance. Using the Bt genes provided the GM cotton with unique in-built protection that has reduced pesticide use by about 80 per cent in the Australian cotton industry.

Is GM a natural form of breeding?

For thousand of years farmers altered the genes of their crops. By selecting plants with desirable traits like higher yields and tastier produce, farmers inadvertently excluded undesirable genes and included desirable genes in each new generation of crop.

These days even conventional breeding employs techniques to cross plants that could not occur without human assistance.

For example, conventional breeding uses chemical and physical means to ‘mutate’ plant genes. These gene mutations may give the plant different, and even desirable, traits. Plant breeders can then select for these desirable traits caused by the mutated gene to breed new plant varieties. Mutations also occur naturally and these are also used in breeding.
Conventional breeding also crosses different species of plants to create hybrids. Plant hybrids are common in agriculture and horticulture and home gardeners would be familiar with hybrid flowers and vegetables.

Conventional breeding can also benefit from GM. For example scientists may think a particular gene is responsible for a certain desirable trait. To confirm this they can develop a GM plant using the gene in question. If this GM plant displays the desirable trait then it is likely the gene is responsible.

Breeders can then go back to the original plant and start breeding to include the desirable gene using techniques like DNA markers that ‘flag’ the location of the gene making it easy for breeders to know if the gene is present or not in each new generation of plant. This method speeds up the breeding of new plant varieties. 

The unique power of GM however lies in its ability to incorporate novel genes into new plants to develop plants with properties that would not be achievable through conventional breeding. This may mean using genes from unrelated organisms such as in the case of insect-resistant GM cotton.

The evolution of plant breeding has been occurring for thousands of years and GM is the latest development. Our ancestors embraced new plant breeding techniques as they emerged and we are the benefactors with a large range of new and improved plant varieties now available to us.

GM is one of a suite of breeding tools that future generations can use to help tackle environmental and human health challenges.

Find out more about Biotechnology for the Community.