Apr 9, 2009

Research Grain

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Field trials with GM wheat

Sophisticated approach for combating loose smut of wheat

Fungi infest wheat and other types of grain. They spread over the seeds and represent a problem, particularly in developing countries, where crofters use a portion of the harvest for sowing in the following year. Scientists from Zurich have developed wheat plants that can protect themselves against such diseases. For this they employ a natural defence system from maize.

In 2009, in the test areas in Thulendorf (Mecklenburg-Western Pomerania) and Üplingen (Saxony-Anhalt ), investigations were carried out to determine whether the new concept against wheat loose smut was also effective under field conditions.

The wheat was developed by the research group of Christof Sautter at the ETH Zurich. Their goal was to use a biological principle that occurs in maize to increase the resistance of wheat against fungi such as loose smut (Ustilago tritici) or bunt (Tilletia caries). These plant pathogens infest grain and spread over the seeds, causing problems in particular in seed production.

Loose smut: a clever parasite

Loose smut completes one lifecycle each year. To start with, infested plants are not outwardly detectable. It is only when they produce ears that a browny-black mass of spores becomes visible. The spores can be spread by wind and rain. When a plant is infected, the fungus penetrates the developing grain. If this is sown in the following growing season, the fungus grows with the germinating plant until it forms a new bunt ball in the ears.

To prevent fungal diseases, wheat seed is routinely treated. This kind of treatment with broad-spectrum chemical fungicides is not permitted in organic farming. There are control measures available here, but they are often very costly and effective only against specific fungal diseases.

Smut fungi are not a big problem in Europe, but they are in some developing countries. The small farmers there cannot afford to buy expensive seed every year, so they use part of their harvest to sow the following year. If this includes grain infected with smut fungi, the farmers are unwittingly contributing to a rapid spread of the fungal diseases and an accumulation in their own crops. Worldwide, according to estimates by the International Maize and Wheat Improvement Centre CIMMYT, smut fungi cause harvest losses of between five and ten per cent.

In principle it is possible to breed fungus-resistant varieties. But this is very time-consuming and depends on there being species available that are crossable and possess suitable resistance genes. This is not the case for all smut fungi.

The Zurich group tried a different approach. They transferred a natural protection method familiar from maize into wheat using genetic engineering methods. The effect is based on a special virus protein. It is produced by a virus that lives in corn smut fungi. The virus uses the protein to ‘help’ its host to protect itself against competition from other smut fungi within the maize plant – thereby preventing the maize plant from being attacked by other fungal infections. The idea was to transfer the genes for the viral defence protein (KP4) to wheat so that it can combat smut fungi in wheat and improve the crop’s resistance. The advantage of this approach is that the KP4 protein has a very specific effect against certain smut fungi, but not against other beneficial fungi that live on the plant or in its rhizosphere.

Field test under realistic conditions

Initial tests in the greenhouse showed that the concept works and can lessen fungal infections. As far back as 1999, Sautter applied to the Swiss authorities to test the developed GM wheat under field conditions. There followed years of bitter discussions, protests, complaints and, eventually, approval for a small-scale trial under extremely strict conditions: the individual plots were covered by weather-proof pollen protection tents and the soil was removed after the end of the trial and sterilised at 120 degrees centigrade. Only eight square metres were planted with the GM wheat.

In 2009 a similar experiment was repeated in Thulendorf and Üplingen. The growth of the fungus and the resistance behaviour of the wheat plants are to be observed under natural environmental conditions. This was only partially possible in the small-scale trial conducted in Switzerland in 2004.

The trial design has a number of plots, each with five variants: two GM wheat lines that produce the KP4 protein, the two isogenic control lines (without the KP4 gene) and a conventional wheat variety that is less susceptible to smut fungus infections. For all five wheat lines, both untreated seed and seed that has been infected with loose smut will be sown.

The project investigated not only the behaviour of the different wheat lines when infected with smut fungi, but also the effect that the KP4 protein contained in the GM wheat lines has on other fungi – both pathogenic and beneficial ones. The root area of wheat plants is home to a number of fungi that improve the plants’ nutrient uptake. First and foremost the project aimed to obtain findings about the way the new resistance concept works. There are no plans to commercialise the KP4 wheat used in the trials.