Ralf Thomas Voegele and Stefan Kunz from the University of Constance have been working in cooperation with the Constance-based company Bio-Protect on this bacterial disease. Together with their team of five students, the two researchers have started their fourth project on how the abatement of the fire blight-causing bacteria can be improved. Fire blight is a bacterial disease that is especially destructive to fruit and ornamental trees. The bacterium Erwinia amylovora destroys the plants. The infestation of plants with the bacteria depends on the interaction between climate, location, plant variety, vitality, bacterial density and cultivation methods. “The period with the greatest risk of infection is spring and summer. The bacteria particularly infect blossom,” said Ralf Thomas Voegele. Fire blight is especially destructive to agricultural plants, in particular to pear and apple trees. The disease occurred for the first time more than 200 years ago in the United States and in Europe in 1957. In 1989, fire blight was detected in the second largest fruit growing area in Germany, the Lake Constance area.

The years 2004 and 2007 were extreme fire blight years in the Lake Constance area and in Switzerland. The team of biologists led by Voegele and Kunz is hoping to glean further details on the fire blight pathogen. “There is growing evidence that the bacteria also occur in tissue that does not display the typical fire blight symptoms. This means that the disease does not break out, which makes the work of the researchers difficult. In the first project, which came to an end in 2007, the biologists took their mobile laboratory to collect field samples and they succeeded in detecting the pathogen so early that further damage was avoided.

The following projects are aimed at the clarification of pathogenesis and epidemiology. An important aspect of the examinations is that the spread of the pathogen depends on apple varieties and cultivation methods. In addition, Stefan Kunz is also investigating diverse substances to see how efficient they are in preventing the infection of blossom. In Germany streptomycin has been used since 1994 in exceptional cases to combat fire blight. Streptomycin use has to be expressly authorised. “The antibiotic streptomycin reduces fire blight by approximately 80 per cent. At the moment, it is the only substance that can keep fire blight in check. However, ecological agriculture requires alternative methods to combat the bacterial infestation,” said Kunz. In addition, the use of antibiotics in agriculture is a highly controversial topic – in particular since the permitted threshold limits in honey have repeatedly been exceeded.

In practice, there are many rumours flying around about alternative plant vaccines or plant strengtheners, but there is no scientific evidence of their effectiveness. “We have established laboratory and greenhouse trials, in which we are carrying out tests on a broad basis. We will then take the most effective substances and test them in field trials,” said Stefan Kunz. Alternative research has so far focused on yeast substances and these have proved to be excellent alternatives. However, these alternatives also have some disadvantages, such as higher cost and the risk of rust in plants. In the new Interreg IV project, Ralf Thomas Voegele and Stefan Kunz’s team plans to expand the current results and focus on substance research as well as on the susceptibility and behaviour of the bacteria. Further focus will also be put on high-trunk plants as a potential source of fire blight and suitable cultivation methods. In addition to EU funding through the Interreg IV programme, the researchers also receive financial support through the Federal Ministry of Food, Agriculture and Consumer Protection.

Source: Südkurier (Elisa Jendrusch) - 22nd April 2008 (P)