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Less chemistry and fresher fruits and vegetables

At Lake Constance, fruit growers have bigger problems to face than ideological discussions on biotechnology and genetic engineering. They need methodological solutions for devastating plant diseases that would help them reduce the use of chemicals.

Harvest waste is the proportion of fruit that cannot be sold. In the 2007/2008 season, this was as much as 5% of the entire fruit harvest, amounting to about 70,000 t of fruit. An important factor leading to this waste is the limited shelf life of the fruit. This can mean that a "record harvest" is not profitable at all. Fruit growers in the Lake Constance region in 2004 experienced exactly this kind of situation with their pear harvest. The sales price for fifty kilograms of "Alexander Lucas" pears, one of the most important pear varieties in Germany, was on average €20 lower than in 2003. The reason for the lower price was not a pear surplus in the EU. Dessert fruit need to be of excellent quality, unlike processed fruit. In the shops, the pears did not correspond to the customers' requirement profile. The pears had cellulite, which was somewhat unappealing. This was the result of excessive after-ripening of the harvested fruit.

Less chemistry and fresher fruit

As apples and pears overripen very quickly, it has been usual for quite some time to treat the harvested fruit with cyclopropene derivatives, a method patented by the North Carolina State University. These derivatives include 1-methylcyclopropene (1-MCP), which blocks the fruit hormone ethylene along with ripening enzymes (see picture), thereby preventing the fruit from overripening and thus reducing harvest losses. However, the effect of these chemicals is variety-specific and depends on the degree of ripeness at the time the chemical is used. The additional costs of 5 percent arising from the use of such chemicals have to be covered by the storage company, which means that the application of 1-MCP is only profitable for premium fruit. It is known that the key enzymes (for pectin degradation, flavour development, etc.) are encoded by several gene families (Höhn et al. 2007). The biotechnological challenges are in the genotypic determination of the state of ripeness as well in the variety-specific mechanisms of action.

The Obstbau-Bodensee Kompetenzzentrum (KOB) foundation close to the city of Ravensburg combines the development of molecular genetic variety determination tests with research on optimal application concentrations and stages of chemical agents (see Kittermann/Streif 2007) such as 1-MCP. Although this is no miracle drug - the loss of water and hence a reduction in fruit quality cannot be prevented - 1-MCP helps producers and transport companies to come as close as possible to the consumers' wish for harvest-fresh fruit, as long as the necessary technological know-how is available.

Fighting plant AIDS

Tony Müller, councillor in the canton of Thurgau, once referred to fire blight (Erwinia amylovora) as plant AIDS. Instead of infecting humans, this bacterium infects pip fruit. In 1962, the devastating plant disease occurred for the first time ever in the USA, and was then introduced in Europe where it rapidly became an epidemic. In contrast to Switzerland and Austria, the German population is not that interested in fire blight, one of the most devastating fruit diseases known. The disease not only affects fruit farmers, but also apiculturists. Fruit plantations treated with the antibiotic streptomycin sulphate leads to the accumulation of the antibiotic in honey produced by bees at a distance of three km from the field that has been treated. The honey from such bees often contains more than the legally valid amount of 0.01 mg/kg. As a result, the honey cannot be sold. "The majority of people - apart from a handful who buy ecological fruit - don't think about how fruit farmers produce their fruit," said Stefan Kunz speaking from experience. Kunz is head of development at the Constance-based company Bio-Protect, a biotechnological research company that has developed the fungus Aureobasidium pullulans to treat fire blight.

However, despite its effectiveness, the Bio-Protect product has some disadvantages. In particular in dessert fruit, and more particularly in the Golden Delicious and Jonagold apple varieties, the fruit look very unappetisingly rusty once they have been treated with Aureobasidium pullulans. Biological apples can still be sold in health food shops – but otherwise, affected apples are just thrown away. Stefan Kunz recommends the additional use of a mixture based on sulphuric alumina. Blossom Protect only affects the blossoms, not the shoots.

The use of antibiotics and plantation clearance is unavoidable until such time as fire blight-resistant fruit become available. Researchers at Agroscope in Wädenswil are trying to produce resistant fruit varieties using molecular diagnostics (see Khan et al. 2007). The infection mechanism of Erwinia amylovora is not yet known. Further basic scientific research such as the research carried out by phytopathologist Prof. Kurt Mendgen at the University of Constance is required to provide further insights.

Fire blight symptom is not always fire blight (left). Some signs can easily be mistaken for other infections, for example those caused by the fungus Nectria (central photo) or the bacterium Pseudomonas syringae (right). According to Esther Moltmann from the Agricultural Technology Centre Augustenberg, laboratory investigations are necessary to detect the bacteria.

The scientific identification of disease cause may help prevent irrational behaviour by fruit farmers. In 2007, fire blight led to more than three million euros worth of damage (BMELV 2008a), despite the fact that the authorities had issued a warning. 500 ha of fruit plantations were destroyed, including 20 ha that had to be cleared in their entirety. The farmers wanted to save money and effort and decided to use streptomycin or the Bio-Protect product in the belief that the trees could only be infected when it was wet or raining.

The farmers mistakenly believed that a dry period prevented the infection of the trees. However, biotechnologists are not very concerned about the stubbornness of the farmers. They can easily find new and potentially more lucrative applications for their developments. The fungus Aureobasidium pullulans produces pullulan, an extracellular glucane with a broad application spectrum. It can be used in food supplements, colourless adhesive, paper bleach, cement additives, floor cleaning of oil contaminations and even as blood plasma substitute.

Fire blight threats will not go away, because the majority of apple varieties are extremely susceptible to Erwinia amylovora. Unlike Blossom Protect, not all anti-fire blight agents have been tested scientifically. “So-called miracle agents might generate good profits, but may not be entirely reliable,” said Ulrich Höfert from the Fruit Alert Service in the Vorarlberg region. In the devastating fire blight year of 2007, it was necessary to fell fifty percent of all standard apple trees. Nowadays, focus is mainly put on reducing the damage, with the exception of commercial fruit plantations. In 2007, the villages and cities were under great pressure, and in 2008 not all data were acquired. Based on these experiences, researchers are specifically focusing on disease-resistant genes and rare varieties.


German Federal Ministry for Food, Agriculture and Consumer Protection, BMELV (2008a): Report about the fire blight situation in 2007.

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