Gene transformation: Gene technology has commonly been used in agriculture for pest and disease resistance and herbicide tolerance, and most recently for developing a greater nutritional value in foods.
The advantage of gene transformation over traditional cross breeding is that only the resistance gene is transferred (along with a marker gene) to an elite variety without the thousands of unwanted genes from the wild-type parents.
It can also take several generations of breeding to remove most of the unwanted genes derived from a wild-type parent. When each generation of breeding can take between 5 and 12 years this accumulates to a very long period of time to develop new resistant varieties with commercial potential.
Method to transfer genes
The most common method to transfer a gene from one plant species to another is to selectively extract the gene and place it and a closely linked DNA marker into a bacterium (i.e. Agrobacterium).
The natural life-cycle of the bacterium involves the insertion of its DNA into the cells of the plant host. Hence the bacterium can be used to naturally infect the host plant and transfer the resistance gene(s) of interest and associated marker into the host plant’s genome.
A tissue culture system is then used to regenerate a plant from a single cell. The plants are tested to determine if the gene of interest has been successfully transferred by testing for the presence of the DNA marker.
The most easily distinguishable markers have antibiotic or chemical resistance and only transformed plants containing these genes will survive when exposed to the antibiotic or chemical.
Gene transfer in apple and pear
There are a few examples of the utilisation of gene transfer (i.e. transgenesis) in apple and pears.
Protocols have been established for reliable genetic transformation and regeneration of transgenic plants in apple and pear.
Early flowering and multiple resistance
In apple, the early flowering trait has been inserted by transfer of a gene from silver birch.
The transgenic plants were then crossbred with a fire blight-resistant wild species and only the transgenic early flowering, fire blight resistant progeny selected.
These progeny were then backcrossed with apple scab and powdery mildew resistant apple varieties and marker assisted selection utilised to identify progeny with all these resistant genes present.
Tree height
In apple and pear, reduction in plant height of the scion variety has been achieved through transfer of size-reducing gene(s) from Agrobacterium rhizogenes into apple and pear rootstocks.
In peach, biotechnologists have had difficulty in developing reliable transformation systems.
GM foods
Perception by the general public of genetic modification has often been negative.
For fresh fruits that are directly consumed, the acceptance of genetically engineered foods by the general public is even more important for successful commercialization than in highly processed foods.
However, GMO foods are the most highly regulated agricultural product and have been monitored for the last 20 years without any detrimental human or environmental health and safety effect.
Gene technology is also commonly used in medicine such as producing insulin used by diabetics.
Tomato
The first commercial release of GMOs in the early 1990s was the Calgene Flavr Savr (pronounced ‘flavour saver’) tomato that could stay riper for longer without deterioration.
Essentially an additional copy of the gene that controls polygalacturonase (PG) activity was inserted into the tomato genome in reverse to reduce PG activity.
The PG enzyme is responsible for pectin degradation in cells walls that leads to softening in fruit. Hence the transgenic tomatoes were able to be ripened normally on the tree but remained firmer for longer than untransformed tomatoes.
Other GM foods
Since then many other genetically modified foods have been released, principally in cropping plants such as soybeans, canola and corn.
In 2012 there were 160 million hectares of genetically modified plants grown worldwide. The majority of these crops have been modified for herbicide (e.g. Glyphosate) or insect (e.g. Bacillus thuringiensis [BT]) resistance.
The BT protein isolated from the Bacillus thuringiensis bacteria is toxic to certain insects of the Lepidoptera family and act by interfering with the insect’s digestive system. It has been widely used in organic agriculture as a natural alternative spray to synthetic insecticides.
Different approaches to improve GMO acceptance
In an attempt to improve the acceptance of GMO in fruit tree crops, researchers are investigating a couple of different approaches.
Place genes in the rootstock
They have been using gene technology to transfer desirable genes into the rootstock rather than directly into the scion variety itself.
Investigations are now been undertaken to determine if the transformed gene is passed through the graft union from the rootstock to the scion.
Transfer genes from compatible plants
Alternatively biotechnologists have utilised a form of gene transfer in apples called cisgenesis.
Cisgenesis involves the genetic modification of a plant with natural gene(s) from a sexually compatible plant such that no foreign genes are used in the genetic transformation process to develop a new plant variety.
Trangenesis on the other hand involves the transfer of gene(s) or part of the gene(s) from non-related plant species or even bacteria or viruses.
Consumers
The term ‘genetically modified’ (GM) describes the altered organisms and products derived from them.
Any food that contains product(s) that have undergone gene transformation must by law be labelled as containing a genetic modified product.
This enables the consumer to make an informed decision if they wish to buy foods containing GM products the same as they make choices with organic and non-organic food products.
Surveys over the last few years have indicated an increasing trend towards acceptance of GM foods.
Feeding the growing population
As the world population increases from the current seven billion, agriculture needs to further innovate to increase food production from the decreasing available area of arable land.
The application of marker–assisted selection and gene transfer technologies provides additional valuable tools for plant breeders to develop improved plant varieties.
Education of the general public on the benefits of GM foods and continued close regulation of its application should help alleviate concerns on the use of foods derived from GM plants and increase future adoption.
For more information and a list of references, see April 2013 Tree Fruit
