Biotechnology is already becoming a powerful presence in our lives, yet most of us know very little about this important scientific phenomenon. Some of us are somewhat put off by technology, and sometimes frightened by it, but we can't keep ignoring it. The purpose of this article is to explain in simple terms what biotechnology is and to illustrate some of the positive aspects of biotechnology that are already benefitting, or are expected to benefit, the New Zealand fruitgrower.

How does this technology work?
All living things carry their genetic inheritance in chemically coded messages or DNA (deoxyribonucleic acid). Under the microscope, DNA looks like a mass of tangled threads. But these threads consist of tiny subunits of DNA called genes. Genes carry instructions, sometimes called "the blueprint of life", for things such as fruit size or skin colour. Genes programme these instructions through arrangements of just four simple molecules - adenine, cytosine, thymine, and guanine. These A, C, T, and G's are like letters of the alphabet - their order "spells" out the language of life.

In nature genes (i.e. pieces of DNA) sometimes "mutate", i.e., alter their chemical structure spontaneously from time to time. These mutations may result in plant cultivars carrying valuable new traits. For hundreds of years, farmers have taken advantage of natural mutations to improve traditional plant lines. For example, the popular apple cultivar "Royal Gala" is a natural mutation of "Gala". However, the time taken from a chance natural mutation to the production of a valuable new cultivar can be many years. But with genetic engineering, scientists are now able to shorten this time considerably.

The term "genetic engineering", sometimes also called "genetic manipulation" or "recombinant DNA", describes how scientists insert new genes into a plant and change its genetic makeup. This process is something like tearing out a page of the instruction manual for one living thing and glueing it into the manual of another. The resulting plant which contains a new gene is called "transgenic".

In the past, we could breed using only closely related species and it took many generations to introduce significant improvements. Genetic engineering allows researchers to shorten this time considerably by inserting only the gene responsible for a desired trait (e.g., pest or disease resistance, skin colour, or fruit size) into a plant, and selecting for that trait. This mimics the evolutionary process but in a highly selective way.

Biotechnology here refers to the commercial application of genetic engineering to the development of new plants. Biotechnology could play a key role in improving our food supply. It could provide us with more nutritious crops and longer-lasting food products that are easier to store and handle. Many genetically engineered plants are already growing in test fields overseas: canola oil with a healthier fat profile; a tomato with longer shelf life and better flavour; alfalfa and cotton with resistance to powerful herbicides; and cotton with resistance to insect pests.

Genetic Engineering and Plant Breeding
Plant breeding is certainly not a new concept. Humans have been breeding and selecting improved plants for centuries, choosing crops with better yield, bigger fruit, or less susceptibility to pests and diseases. This is particularly true of annual crops such as wheat and corn, where many of the cultivars now grown bear little resemblance to those of even last century.

However, progress in the improvement of long-lived tree crops by breeding has been much slower than for annual crops, despite the wide range of characteristics available. The main problem is the length of time from the germination of seeds until the production of fruit. Promising selections then need to be tested on rootstocks, in different locations. The whole process from start to finish may take as long as 15 years.

The major challenge presently facing breeders is to shorten the length of time required to develop new cultivars. This is where the use of biotechnology can assist. The objectives of plant breeding and improvement are basically the same, whether they are achieved by conventional breeding methods or genetic engineering. The difference between the two lies in the speed and accuracy with which new cultivars can be achieved. If an established plant cultivar needs a disease-resistance gene, the genetic engineer will be able in the future to simply splice it in without disturbing the 100,000-odd genes already in the plant. However, for the conventional plant breeder, the gene for the characteristic needed comes together with all the other genes of that plant - many of which will dilute the desirable qualities of the original cultivar, or even give undesirable qualities. It can take many years, and five or six back-crosses to the original cultivar to sift out the unwanted genes and recover something resembling the original genotype of the parent.

Much emphasis has been placed on the development of genetically engineered "designer" plants where new genes are added to the plant, or existing genes modified. But while the addition of new genes is significant, the powerful new techniques developed are the real breakthrough. The knowledge gained helps our understanding of the biological basis of conventional plant breeding, and will open the way for a whole new era in plant breeding.

Many genetic techniques are already helping plant breeders to speed up the breeding process. A good example of the interaction between plant breeders and biotechnologists is in the area of developing new pest and disease resistant apples.

Developing New Pest and Disease Resistant Apples
At present most pests and diseases are controlled by applications of chemicals. However, international markets are placing increasingly lower residue limits on imported fruit and there is greater consumer awareness about potential environmental and health issues associated with chemical sprays. In response to these concerns, HortResearch has a diverse research programme aimed at investigating the complete range of options available to replace or supplement chemical sprays to ensure environmentally sustainable supplies of safe, nutritious, affordable food.

The most effective long term and environmentally friendly way of reducing spray use is to develop fruit cultivars that are resistant to pests and diseases. Breeding new cultivars by conventional means can be very hit and miss, and take many years. To speed up the process of developing disease resistant cultivars, HortResearch plant breeders and molecular biologists have combined their skills. Genetic manipulation should give the same result more quickly than traditional breeding, but also give greater control. It should mean that the time needed to transfer the natural resistance to apple scab found, for example, in some crab apples to an export apple cultivar like "Gala" or "Braeburn", can be cut in half.

Developing resistant apple cultivars starts with the conventional plant breeder. Freshly germinated apple seedlings, from crosses between susceptible and resistant parents, are exposed to pests and diseases. Information on the resistance or susceptibility of these seedlings to a particular pest or disease, together with leaf samples for DNA analysis, are sent to another group of researchers in HortResearch who are developing an apple gene map. The data provided by the plant breeders helps to locate "DNA markers" which are near each resistance gene on the apple chromosome. (The gene map will also include markers for other important traits.)

These DNA markers will be used in future to provide apple breeders with information on the resistance potential of young seedlings before this potential has been expressed. Such early progeny screening and selection of elite seedlings before they are planted out in research orchards should enable a significant reduction in the requirement for land and plant maintenance, as well as providing breeders with specific information needed to design subsequent crosses.

This information on DNA markers will also be used by other molecular biologists to isolate the resistance genes from special "libraries" containing apple DNA. These genes are the key to a range of new disease control methods including transferring genes into other apple cultivars to speed up the breeding process.

The whole process is also being helped by HortResearch's development of an extensive collection of old-fashioned apple cultivars which are no longer used commercially, and apple lines collected from around the world both in the wild and from other breeding programmes. This world-first collection will increase the range of genes available both for use in conventional breeding and for genetic engineering.

Other Uses of Biotechnology

DNA markers in Kiwifruit
DNA markers are also being developed to assist our kiwifruit breeders. Kiwifruit has separate male and female plants, and at present plants can be distinguished only once they have flowered, usually after several years' growth. This means that conventional plant breeding programmes are very inefficient as half the seedlings grown are non-productive males. Identification of sex-linked markers will provide a valuable selection tool for breeders in their search for quality female selections. In addition, mapping of markers linked to other fruit-related characters will enable the breeding programmes to be planned and focused more efficiently in all areas, from the initial choice of parents, to the early culling of undesirable phenotypes and the early identification of selections.

Cultivar Identification: "DNA Fingerprinting"
Another use of biotechnology that will benefit all fruit breeders is the development of methods for the identification of clones and cultivars. One method, "DNA fingerprinting", identifies individuals by the unique profile produced when their DNA is separated into a series of fragments and resolved into size classes. The end result is a profile rather similar to the bar code that identifies items in a supermarket. DNA fingerprinting is used widely in forensic science to identify individuals involved a particular crime. Similarly, these DNA profiles can also enable unique cultivars or clones to be identified unequivocally, and the technique has potential in the specific identification of plant cultivars and their subsequent protection.

Disease Detection
Early detection in the field plays a major part in being able to control diseases. Using DNA technology, sensitive detection methods have been developed which can detect the bacteria causing fireblight even when there are no symptoms evident in an orchard. This ability has meant that we are now able to export our apples to Japan.

Alternative Pest and Disease Control Methods
As well as the development of molecular markers for natural resistance genes, HortResearch scientists are trying to find other ways to give plants resistance to pests and diseases.

Fungal Diseases
Root-rotting and fruit-rotting fungi are being studied, using a combination of conventional and molecular techniques, to find ways to disrupt normal infection processes. Investigations are being made of the natural resistance mechanisms operating in plants. These mechanisms control the development of rots, such as production of enzymes which are active against fungal cell walls, or products that inhibit critical fungal enzymes. The genes for these enzymes may be used in developing disease-resistant plants.

Virus Diseases
Biotechnology is also helping in developing control strategies for virus and viroid diseases on many horticultural crops. These agents can adversely affect fruit size, appearance, sugar content, yield and flower break. For example, the tamarillo mosaic virus causes blotchy fruit and leaves, and is the major obstacle to exporting tamarillos. DNA technology is being used to overcome these problems: by splicing the viral coat protein gene into the tamarillo plant, the plant is made resistant to the virus.

Insect Pests
Insect pests are a major cause of crop damage and can also pose quarantine problems on exported fruit. Alternatives to the currently used chemical sprays are urgently required. The bacterium Bacillus thuringiensis (Bt) produces a crystal protein which is toxic to selected insects but is completely safe to humans, other species and the environment. Bt is currently used as a bioinsecticide as an alternative to chemical pesticides. Scientists are working towards putting the crystal protein gene into plants to give them "inbuilt" insect resistance.

Fruit Quality
Fruit quality refers to all the factors such as colour, flavour, texture, size and shape, which are the main determinants of fruit acceptability, as well as storage and shelf life. Our ability to control these factors would give us a competitive advantage in export markets. HortResearch scientists are studying many aspects of fruit quality, including colour development and the ripening process. A method developed in the US on tomatoes, in which scientists insert a mirror-image of the gene involved in fruit softening into the fruit, could be adapted for fruit in this country, particularly where poor storage and shelf life cause problems for exporting the crop. The U.S. studies have found that these genetically engineered fruit were less prone to rotting.

Safety
There have been concerns raised about genetically modified plants escaping into the environment and competing with wild plants. But as has been explained earlier, biotechnology usually only involves the insertion of one or two genes (i.e. pieces of DNA) into an existing cultivar. There is less risk involved in this than in conventional plant breeding where a number of undesirable characteristics may show up in crosses. Also, every gene is equipped with a region of the DNA code, called a promoter, which switches the gene on and off, and specifies when, in what cells and in what amount the gene's protein or enzyme is to be made (O'Neill 1994). These "DNA switches" can be tailor-made for specific requirements and can even be externally controlled.

Furthermore, before researchers can even start to experiment in genetic engineering, their plans must be approved by a regulatory body set up in New Zealand to determine which projects are acceptable. All experiments involving transgenic plants must take place within strictly confined glasshouses. Before releasing transgenic plants, it is necessary to carry out a risk assessment to determine whether the transgenic cultivar will behave differently from a conventionally bred cultivar. Assessment procedures are coordinated and regulated internationally by various organisations.

Transgenic plant systems have now been developed worldwide for more than 30 crops as diverse as maize, oats, rice and cotton through to grapes, kiwifruit, papaya and apples. The overwhelming conclusions from nearly five hundred field test experiments on genetically engineered plants in the US and Europe are that newly introduced genes - including those for quality improvement and for control of insects, weeds and plant diseases - are stable, inherited and are expressed like any other plant gene (Fraley 1992).

Conclusion
Medieval philosopher de Toqueville said "people will believe a simple lie in preference to a complicated truth." For most people, biotechnology is about as complicated as science gets. But biotechnology is something people should be informed about because it is extremely potent in what it can do.

Technical advances are already providing significant commercial benefits to growers, processors and consumers. We believe the growth in the world population and in the demand for food, and the clear consumer preference for environmentally sustainable agriculture will extend biotechnology's role in food production.

The general opinion of the experts is "that biotechnology is simply a better way of doing what breeders have done for millennia in trying to improve agriculture" (Naisbitt & Aburdene 1990). While biotechnology is unlikely to completely replace conventional plant breeding, it certainly has a place in enabling breeders to achieve their objectives more quickly, safely and accurately. The development of new cultivars with pest and disease resistance and/or improved fruit quality will enable the New Zealand fruit industry to maintain and enhance its competitive advantage in export markets.

References:
John Naisbitt and Patricia Aburdene. Megatrends 2000. Pan Books. 1990.

Graeme O'Neill. Dinner at the DNA Cafe. Time. January 17, 1994. pp 38-42

Robert Fraley. Sustaining the Food Supply. Biotechnology. Vol 10. January 1992. pp 40-43

Source:
The Orchardist, May 1994, Vol: 67, Number: (4):40