Wild spuds and the silence of the genes

The potato industry reflects on gene technology


Challenges that the potato producer will face in the future include the effect of climate change on yield, quality and pest control, sustainable and effective use of resources such as water and ground, provision of safe, healthy potatoes to the consumer and the need to provide consumers with potatoes that satisfy their preferences.

Cultivars developed for the future will play a critical important role in addressing the abovementioned challenges.

Cultivar development

Remarkable progress has been made with conventional potato cultivation since the first cross-pollination more than 100 years ago, especially in terms of yield. But despite the fact that genes for resistance to major diseases do occur in wild potato species, most potato cultivars are still not resistant to most diseases. The potato industry recently reflected on the potential of different techniques available for potato breeders. The technology currently available is given in Figure 1.

Conventional potato cultivation

It is speculated that 80% of all cultivars that existed in 1980 were developed from parents that survived the late blight epidemics of the 1800s. This has given rise to the restricted genetic basis of current breeding programs. The solution to expand the genetic basis would be to use some of the characteristics that exist in wild species. However, there is a restraint because the original breeders not only survived the late blight epidemics, they were also all tetraploid, i.e. each cell contains four sets of chromosomes. Wild potato species, on the other hand, are diploid, i.e. each cell contains two sets of chromosomes. To incorporate the properties of diploid plants in commercial tetraploid plants, self-pollination of parent lines is required. However, there is a gene in potatoes that prevents self-pollination, so current commercial cultivars are all tetraploid. The biggest challenge of cultivating tetraploid potatoes is surely the fact that for each characteristic in a plant, there are four genes. Adverse genes in hybrid seedlings often do not immediately appear. This means that a large number of new hybrid seedlings have to be evaluated for many years and under different conditions before they can be commercially planted. The fact that current cultivars are tetraploid also means that hybrids cannot be propagated with botanical seed. Vegetative propagation by daughter tubers means that tuber borne diseases can be spread through the seed potatoes.

If potatoes could be diploid it would be easier for breeders to exploit the properties of wild potato species than in a tetraploid breeding program. The possibility of cultivating diploid potatoes has received a major boost after researchers in Japan and the Netherlands have identified a plant in which the gene that prevents self-pollination does not exist. The University of Wageningen and a company named Solynta exploited the possibility and in 2017 the first diploid hybrids were introduced. Meanwhile, other breeding companies have also established diploid breeding programs. Full-fledged commercial cultivars are expected to be released in 5-10 years. See also: CHIPS Sep / Oct 2017 Seedlings or seed potatoes?

No commercial F1 hybrid cultivar has been released at this time. So, we can only speculate on how the innovation can affect the potato industry. The hybrids are developed by conventional breeding techniques, similar to F1 maize cultivation. Vegetative propagation of potatoes is a well-established practice and it is unlikely that the practice will be completely replaced by seedling production. The fact that F1 hybrids are produced with botanical seed makes international trade safer than seed potatoes. The biggest advantage of F1 hybrid potatoes is that it will be easier for breeders to transfer untapped characteristics of wild potato species to commercial potato.

Gene manipulation

This technology involves changing a plant’s genetic material through technological intervention by humans. The first genetic manipulation techniques involved transferring a gene from one organism to the recipient plant’s genetic material through a bacterial cell. Since then, many new genetic manipulation techniques have been developed and applied. Cisgenic manipulation involves transferring a gene of a plant that is genetically compatible to the recipient. Intra-genetic manipulation involves changing the gene of a plant that is genetically compatible with a recipient plant, and then transferring it to the recipient plant. Genes are transmitted by a bacterial cell or, by a so-called gene gun. In all genetic manipulation techniques, man has no control over where a new gene is inserted in the genetic material of the recipient plant and it is also not known what the consequences may be.

Since the first genetically manipulated (GM) plants were release in the early 1990s, transgenic maize, soy and cotton are grown at 170 million he in 29 countries. Several genetically manipulated potatoes have also been released in other parts of the world, but to our best knowledge none of these are produced commercially.

Genetically manipulated (GM) potatoes

NewLeafTM from Monsanto was released in in the USA in 1995 and was resistant to the Colorado beetle and PLRV. The gene for resistance to the Colorado beetle was derived from the bacterium Bacillus thuringiensis (hence the name Bt potatoes). Farmers were eager to plant NewLeaf and after just four years more than 20 000 hectares were planted with NuLeaf! But after another two years, the area planted with NewLeaf dropped to zero. The reasons for this dramatic rejection of the cultivar were manifold, but included: the release of a new insecticide against the Colorado beetle and the public’s requirement that genetically modified food should be handled completely separately from conventionally grown foods

Michigan State University and the Agricultural Research Council developed Bt-Spunta with resistance to potato moth and in 2010 applied for registration for exemption in South Africa. The Department of Agriculture, Forestry and Fisheries has rejected the application in spite of the fact that the application has met all the requirements from a technical point of view. At that stage, the South African potato industry felt that the industry was not yet ready for genetically modified potatoes. Almost 15 years later, Amflora from BASF Plant Science was released for industrial starch production in Europe. Although the safety of Amflora was thoroughly tested and proven, it still took 12 years for it to be approved for production in Europe. Still, the European public did not accept the product. As a result, BASF decided in 2012 to withdraw Amflora from Europe and concentrate on the release of Amflora in the Americas and Asia. InnateTM potatoes were developed by “RNAi gene silencing” technology to turn off (or silence) the gene responsible for browning of cut potatoes, thereby reducing food waste. InnateTM also has reduced levels of asparagine and reducing sugars that reduce the formation of acrylic amide. In the US and Canada, Innate was declared “safe and nutritious” by governments. McDonald’s, however, has declared that they will not use Innate potatoes due to pressure from the Food and Water Watch organization.

Social acceptance of genetically modified food

Currently, the European consumer determines to a large extent which genetically manipulated crops are planted on a large scale in the world. There is less resistance to crops intended for biofuel, animal feed or industrial purposes, hence GM maize, soy and cotton are planted on such a large scale. In contrast, GM is food that is eaten directly by humans, e.g. rice, wheat and potatoes, is not acceptable.

The European’s resistance to GM technology has an impact on world trade

GM crop regulation in the US is more flexible than in the EU, with the result that the US produces most GM crops. At the same time, large amounts of food are exported from the US to the EU. Changing the regulation of GM crops can therefore have a major impact on trade. A good example of this was in 2006 when small quantities of GM rice were found in a commercial consignment from the US to Europe. In spite of the fact that the USDA and the US FDA found that GM rice has no human health or environmental impact, the entire consignment was not allowed in Europe. As a result, US rice prices fell immediately and globally. Also, the GM rice developer had to pay $750m to farmers as compensation for losses

The opinion of the scientists

The sentiment regarding the safety of genetic manipulation varies from strong support to disapproval. Support is based on the potential benefits that technology can have on food production with increased nutritional value and reduced use of pesticides to feed the growing world population. Scientists rejecting the technology are concerned about the unintended, potentially negative effects of technology on the environment and human health over the long term. The concern is mainly based on the fact that man does not control where in the genome of the recipient plant, the new gene is established.

Regulation of GM crops in the European Union

On July 25, 2018, the European Union Court of Justice decided that all organisms developed by any form of genetic engineering should meet the same requirements as conventional transgenic plants, that traceability measures and techniques should be in place and that all products containing GM ingredients should be labelled. Opponents of the GM technology’s relief were huge. The disappointed comment of the European Biotechnology Association EuropaBio, and other advocates of GM technology was: “In addition to affecting global agricultural trade, this judgment has significant consequences for EU innovation”.

Deciding on the local potato industry for gene technology

There are several reasons why the relatively small potato industry in South Africa can not invest in genetic manipulation techniques on the medium to long term:

Gene technology is only part of a breeding program. The industry has already decided in 2011 not to invest in breeding programs because there are enough role players who have already been successfully involved in cultivar development.
Genetically modified crops are unacceptable to our southern African trade partners and it is important that exports of both ware- and seed potatoes are expanded to our neighbouring countries.
The industry recognizes the potential of F1 hybrid potatoes, especially to build genes for disease resistance in commercial potatoes. 

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Issue 46


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