Fire-blight resistant apples

Gessler and his collaborators were using so-called cis-genetic engineering. Additional genes are incorporated into cis-gene organisms using the biotechnological methods available. However, these are not foreign to the species, as in the case of so-called transgenic organisms. Instead, the apple only receives genes from another variety of apple. Although the gene was marked with other genes that were foreign to the species to discern whether the gene transfer was successful, the researchers managed to remove these foreign genes from the genome of the Gala apple afterwards so that only the wild-apple genes remained.

The researchers tested the fire blight resistance properties of the cis-gene apple trees in the greenhouse at the Agroscope research facility in Wädenswil and in Germany by infecting them with fire blight. The results revealed that the resistance gene took effect and prevented the trees from becoming infected.

All down the drain?

Although Gessler has now been able to reap the fruits of his years of research and development work, he does not believe that fruit farmers will ever grow these cis-gene apples. On the one hand, there is a still a moratorium on genetic engineering in Switzerland, banning the cultivation of genetically modified organisms (GMO), which also affects cis-gene crops. “Moreover, there is still too much opposition to GMO in Switzerland,” he says. And, unlike in the USA, here in this country and the EU we don’t assess individual products for approval, but rather the technology used while growing them. “Unless the attitudes and legislation change, the cis-gene Gala apple will never be grown,” the plant pathologist sums up.

Gessler is not a GMO hardliner looking to push genetically modified crops at all cost. “In the case of crops like the banana, cassava or apples, which can be reproduced via clones, however, the use of genetic engineering makes sense,” he says. Consumers have to realise that an organically grown Gala apple is treated with copper and sulphur at least twenty-five times, which has a serious impact on the soils, air and groundwater. Scab and fire-blight-resistant cis-gene Gala apples do not have to be treated in this way, making them more environmentally friendly than their bio-counterparts.

Breeding in the resistance gene via conventional cultivation, however, takes too long, says Gessler. The Gala variety would have to be crossed with a wild apple and the undesired properties of the wild apple bred out again in subsequent generations, which can take many decades and ultimately results in a new variety.

More resistance genes to make doubly sure

Another obstacle stands in the way of growing cis-gene apple trees in the foreseeable future: “Although the gene now implanted works, it only takes one mutation for the pathogens to get around this resistance, which can happen very quickly,” Gessler points out. Consequently, more resistance genes need to be added to the cis-gene Gala apple to have a cumulative effect. As a result, the probability of the pathogen circumventing the infection protection drops exponentially. Only then can we really begin to consider planting cis-gene trees on open land. Agroscrope will continue to conduct research into this multiple resistance as Gessler is retiring from ETH Zurich in April 2014.

This means that the threat to fruit cultures from fire blight has not been averted in the short run. “Another epidemic might break out this spring,” warns Gessler. Warm and wet weather shortly before the flowering season are ideal conditions for the bacteria that cause fire blight to multiply at an explosive rate.