Jul 17, 2003
Research Live
SiFo project: Fructan potatoes - Effect on pests
Fodder for the munching machines
“They are incredibly fit. It’s only spiders that give them a hard time.” Pia Roppel is almost respectful of the Colorado potato beetle. Hundreds of larvae are scuttling about in the bowls on the table. They eat incessantly. Every two days Pia Roppel provides a fresh bunch of potato haulms. She wants to find out whether certain potatoes cause the beetles and larvae to develop differently.
Trial fields with transgenic fructan potatoes. Twelve potato strains are tested on each plot: six transgenic strains, two unmodified wild types and four conventional varieties of potato. The different strains can be identified by flower colour, flowering time and vigour.
Bigger beetles? Pia Roppel counts out twenty larvae and puts them in a net bag (top). This is then attached to the potato plants (Bernd Hommel, bottom). The larvae are weighed every two days. The aim is to determine whether the larvae feeding on the fructan potatoes show improved development.
Egg laying. After mating (left), the female potato bugs deposit a total of approximately 1,200 eggs on the underside of the leaves.
First, the larvae consume their own eggshells and then ascend the leaf sprouts while eating them. The plants may be eaten bare in the case of heavy infestation, causing great loss to yield.
Pia Roppel beside one of the wooden cages which each enclose a plot containing Colorado potato beetles and the potato variants.
Colorado potato beetle larvae in the laboratory are fed on leaves from different potatoes.
Counting nematodes. Transparent pots are used to study the occurrence of nematodes worms in the root area of the potato plants.
Leaf discs of the different potato variants were infected with the Phytophthora fungus. After a few days it was noted where their fungal mycelia had best developed.
The bowls are in a safety laboratory at the Federal Biological Research Centre in Kleinmachnow on the outskirts of Berlin. Some of the leaves which the larvae are eating come from genetically modified plants.
These potatoes were developed at the Max Planck Institute for Molecular Plant Physiology in Golm. They produce fructan, a special carbohydrate which has beneficial health effects. Two new genes have been inserted into the potato. They are responsible for the production of enzymes which convert the potato’s own sugars into fructan.
Although there is some doubt as to whether these potatoes will ever be marketed, researchers at the BBA are interested in investigating the possible consequences of actually cultivating fructan potatoes.
“For the creatures which feed on potatoes, fructan represents a new nutrient”, explains project director Bernd Hommel. It is possible that some pests will develop better as a result. This would mean that more chemical pesticide sprays would have to be used. A knock-on effect like this would be a serious drawback for Hommel and his team.
Several pests are involved in the trials, including the voracious Colorado potato beetle. This pest was introduced from the USA around 1920 and has since spread throughout the world.
Larvae in the bag
The BBA trial fields are located seventy kilometres away from the institute in the Brandenburg village of Dahnsdorf. Trials of genetically modified fructan potatoes have been conducted here amongst the innumerable plots since 2001. On each of the four fields there are six different strains of fructan potato as well as two unmodified wild types and four conventional varieties by way of comparison. In total, 96 tubers of each have been planted in a specific pattern.
In laboratory experiments it was apparent that the Colorado potato beetles preferred some of the transgenic strains. The researchers now plan to test this finding in the field.
With this in mind, Pia Roppel and Bernd Hommel have prepared a new trial. Twenty of the institute’s own beetle larvae are placed in a net bag, which is then attached to plants of different strains. The larvae are weighed every two days. This will show whether the beetles feeding on the fructan potatoes grow faster.
More sugar, more eggs
A similar experiment has already been running for some time. It is easy to spot from the large wooden cages which surround small trial plots containing the twelve potato variants. Two hundred and forty beetles have been released in each of the six cages immediately after hatching from the soil. The number of clutches of eggs laid by the females on the different plants over a period of several days is counted.
“It seems that the females prefer certain potato variants because of their nutritional composition,” says Pia Roppel. “It is well known that potatoes with a high concentration of sucrose have a positive effect on the development of the beetles.”
Forced extension of the trial
Other pests such as nematodes or Phytophthora fungi, the pathogens of late potato blight, could also benefit from fructan potatoes. Hundreds of leaf discs are systematically infected with the fungus. These experiments are only being conducted in the laboratory. In the field the risk of a Phytophthora epidemic would be too great.The BBA researchers are systematically searching for further potentially significant effects of fructan potatoes. In realistic growing conditions their appearance, tuber size, yield and starch content and also their overwintering ability in the soil are being examined and compared with conventional tubers.
However, the results have to be regarded with caution, since the database is currently rather small - partly because the trial fields were destroyed last year. Bernd Hommel hopes that the field experiments will be extended by one year. “We really need a three-year growing period to fully support our findings.”
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