Oct 21, 2003

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Genetically modified apple trees

“… they don’t spread unchecked”

The Federal Centre for Breeding Research on Cultivated Plants (BAZ) in Dresden-Pillnitz developed genetically modified apple trees with the aim to improve their resistance to major apple diseases. GMO Safety spoke to Viola Hanke from the Institute of Fruit Breeding in Dresden-Pillnitz about chances of genetic engineering in apple breeding and the common fear that the transgenic apple trees could spread unchecked.

GMO Safety: An apple goes straight from hand to mouth; it is a symbol of healthy and unadulterated food. In the minds of most consumers there is a contradiction between “healthy” and “genetically manipulated”. Do transgenic apples actually stand a chance in Germany?

Viola Hanke: I’m afraid the symbol of unadulterated food gives no indication of what actually happens during the development of the apple on the tree. Before it reaches the supermarket shelf, the apple has already survived several fungicide and insecticide applications, plus a whole host of other chemical treatments. Is that still unadulterated and healthy?

Personally I see no contradiction at all between genetically modified and healthy. On the contrary, genetic engineering provides opportunities to reduce the application of chemical pesticides and with it the amount of residues contained in fruits and in the soil, and even a reduction in allergens.

As to whether transgenic apples stand a chance in Germany, one cannot of course consider Germany in isolation. In this context we have to look at both the world market and the European market, since globalisation affects apple production too. At present we are trying to develop and evaluate a methodology for the genetic approach. The implementation stage, i.e. the registration of a genetically modified variety for cultivation, is still a long way off. Consumers cannot expect to see genetically modified apples on the shelves within the next twenty years.

GMO Safety: Varieties with high resistance to fire blight, apple scab and apple powdery mildew have been bred at your institute using conventional methods as well. What advantages does the genetic approach offer?

Viola Hanke: The genetic approach provides the opportunity to insert a single desirable trait, such as resistance, into established varieties. In conventional breeding, two different varieties with different genomes are crossed with one another, producing a number of progeny with very different traits due to the recombination of genes. It is impossible to find even a single progeny which is completely identical to the mother variety apart from one additional trait. This is where the genetic approach has the advantage. Resistant varieties produced by conventional breeding methods in Pillnitz are of great importance to specific local crop-growing areas and to certain forms of fruit production. But they fall short of the quality criteria currently required of a global variety. That may change with further breeding.

National groups working in the field of genetic engineering therefore prefer to focus on improving a global market variety. You have to understand that world production is dominated by just four varieties of apple. By the year 2010 it is estimated that the most important varieties, which are produced in various countries, will be available for 12 months of the year. These varieties, incidentally, are all susceptible to diseases.

GMO Safety: Critics fear that the transgenic apple trees could spread. What hybridisation partners or potential for dispersal does the cultivated apple actually have?

Viola Hanke: One dispersal route for transgenes in apples is via pollen and seeds. The apple is pollinated by insects not by the wind. The pollen is comparatively heavy and falls to the ground. Insects can only reach the transgenic pollen by visiting the flowers.

The apple can be crossed with partners from the genus Malus, which includes other apple varieties and wild species. Hybrid products can also be obtained through experimentation by crossing with other species from the Rosaceae family, although this does not occur in the wild. Furthermore, the apple is self-sterile and does not produce progeny with pollen from its own cultivar, or even from a range of related varieties, due to the sterility genes. From a botanical perspective, therefore, damage to other agricultural or horticultural land resulting from transgenic apple pollen can be ruled out. Apple trees do not cross with grapevines or oilseed rape.

GMO Safety: How probably is a spread via apple seeds?

The apple fruit itself cannot be contaminated by transgenic pollen, since the flesh of the fruit develops from the receptacle, or base of the flower, which is not genetically modified, as opposed to the seed. During pollination with transgenic pollen, the genetic modification is actually only present in the seed. But the probability of such seeds occurring is very low, since only a tiny quantity of the large amount of pollen arriving on the stigma will germinate and only one pollen grain will fertilise the ovum. If a transgenic pollen grain fertilises the ovum, then only one in ten of the seeds present in the core will be transgenic.

That single seed must then manage to grow into a plant. Seeds can be dispersed in the faeces of foxes, wild boar and hares and above all by humans. Seedlings are not found in managed orchards and allotments. Seeds are able to germinate on the edges of woodland if there is sufficient light. But it is unlikely that this would result in standing crops, due to the environmental conditions and competition from other plants. If this were the norm, we would not have to protect and map the native wild species Malus sylvestris, or crab apple, in fact there would be vast forests of it. The crab apple has played only a small part in the development of the modern cultivated apple. The main ancestor is Malus sieversii, a native of Central Asia, which arrived in Europe via the Silk Route, where it hybridised with other species.

Furthermore, seed contamination caused by the dispersal of transgenic apple pollen is not an issue, unlike in other agricultural crops, because with apples the seed is not used; apples are vegetatively propagated by grafting a scion onto a rootstock. Only the breeder harvests the seed, which he uses to breed new seedlings.

GMO Safety: Thank you for talking to us.