The active cultivation of crops probably began twelve thousand years ago in the Middle East. The hunter gatherers, as the people were called, used the “just in time” system, that means they hunted the animals needed for food and gathered any food plants that were available naturally, without thought of storing them for any length of time. After a period of particularly severe drought had decimated the naturally occurring crops the more prudent villagers began to keep back some of the seed for planting the following year. The practice spread and before long the farming of crops became a world wide activity.

Gradually new types of crops able to survive in a specific environment evolved by a process called natural selection. In natural reproduction the offspring receives one set of chromosomes from the female plant and one from the male, but the genes in the newly produced DNA interact differently with each other in each offspring and therefore there are variations and no two offspring are the same. As farming grew more sophisticated it became possible to cross breed plants to produce progeny that fulfilled a particular purpose. This was done on a trial and error basis as farmers had no knowledge of how the process worked. However, cross breeding can take many years and plants will generally only breed with the same species. Domesticated maize is quite different from its wild origins as it has larger heads, thus producing more seed to feed greater numbers of people. Hybridisation of plants is generally more reliable and produces offspring that will each have similar characteristics, but they are generally infertile and do not produce seed and have to be reproduced by cuttings. Crossing crops with wild relatives gives greater access to genetic variation, but unwanted genes are introduced by this method which are then back crossed again and again until the desired effect is achieved.

Many wild plants are toxic to human beings as they have to defend themselves in order to survive. Some use spikes and spines, but many use naturally occurring chemicals. Cooking breaks down many of the toxins and helps to release more nutritive value from food, allowing a greater choice to be consumed. Such staple foods as Potatoes and Red Kidney Beans are poisonous before they are cooked and Cassava is a source of Cyanide. The pharmaceutical industry has been using chemicals such as Pyrethrum, found naturally in plants, for many years, but the increasing demand for more pesticides or medicines has meant that they have had to find a way to synthesise these chemicals.

As the countryside is eroded by the growth of urban communities and industry, so different types of crops are needed to be able to survive in the increasingly polluted atmosphere and the lack of space. In twenty years time there will not be enough food being produced to feed the growing world population.

How would it be possible to speed up the process?

Scientists studying Crown Gall Disease on fruit trees found that the tumour like growths were caused by bacteria entering the plant through a wound making the plant produce hormones. These hormones upset the natural growth pattern and cause the cells to produce growths or galls containing opines that are special amino acids which the bacteria feed on. It was found that these agrobacterium tumefaciens have a special type of DNA consisting of two separate parts; one chromosome and a Ti or tumour inducing plasmid. A plasmid is a separate piece of DNA able to replicate independently and all or part of this can be transferred to another cell without harming the bacterium. Vir or virulence genes on the Ti plasmid are used for the transfer process as these encode the proteins needed for the assimilation of the opines produced in the tumours on the trees.

In genetic engineering the hormones and opine genes on the Ti plasmid in the bacterium are replaced by new genes with the required characteristics and these are transferred into the host plant without causing disease. However this only works on one cell and several methods are used for changing the genes in a whole plant.

1. Micro projectiles coated with the new DNA can be fired into the plant cells.

2. Seeds are germinated and the seedling leaves dissected and incubated with genetically modified agrobacterium. The DNA is transferred from the bacterium into some of the leaves. After killing the bacterium with antibiotic the leaves are removed onto a tissue culture medium to create new plants. Only a small proportion of the new plants will contain the engineered DNA.

3. Sterile leaflets are grown on a liquid medium with hormones to induce rooting and the bacterium is added which then transfers the engineered DNA to the new plants.

One of the genetically modified crops already on the market is tomatoes that have had a new gene added to modify the chemical that causes softening, thus the plants can be ripened for longer, giving a better flavour and producing a more tasty paste. Several types of plant have been engineered with the insecticidal toxin gene of Bacillus thuringiensis so that insects attacking these crops are killed. The problem is that the insects may eventually mutate to become immune to the insecticide. Soy beans have been modified to be resistant to herbicides. Growers used forty per cent less herbicide and had a six per cent increase in yield and increased soil moisture. Oil seed rape has also been modified in this way with increased yield. Crops can also be protected against fungi, bacteria and viruses by genetic modification.

In order to meet the increased production needed for the growing world population genetic modification is being used in many new ways. Photosynthetic genes have been transferred from maize to rice giving a twenty per cent increase in yield. A dwarfing gene from wheat can now be transferred to rice to give more yield. However, rice does not contain vitamin A and, as fifty per cent of the world population depend on rice, a golden rice has been engineered from daffodil genes, which supplies the B carotene precursor to vitamin A. Salt can build up in irrigated soils rendering the farmland useless, therefore a transgenic rice has been produced that grows in seawater. Rice that originally grew in water is now being developed to be grown on land. Genes from desert plants can be used to produce crops that withstand drought.

Genes for antigens in vaccines can be introduced into food crops to stimulate the body against pathogens. A biomedical glue can be produced by inserting the glue producing genes from mussels into plants such as tobacco plants, for use in tissue closures, bone repair and marine engineering. Genes encoding fatty acids could be added to oil crops to make plant oils used in lubricants, paints, detergents and nylons. Bio degradable plastics can also be manufactured by genetically modifying the starch structure in plants.

It is now possible to introduce genes from other species, such as insects and animals, into plants to produce the required effect. The ethics of these processes must be decided by individuals in order to reach their own conclusions. Who knows what will happen in the future? © GMH