Corn grain mould used as pesticide

In the early 1960s more than 100,000 turkeys died in Britain of cancer of the liver. Eventually, researchers identified mouldy peanut flour from Brazil containing large amounts of aflatoxin as the cause of this mysterious 'turkey X' disease. Even today the toxin is regarded as one of the most virulent natural carcinogenic substances.

The tasteless toxin is produced by the mould aspergillus flavus. It grows in hot, arid regions, in the south-west of the US and in many regions of Africa and Asia. In Third World countries, particularly, this dangerous paintbrush-shaped mould is ubiquitous. This may be one reason for the high rate of liver cancer in Africa. "Our colleagues from the IITA in Nigeria recently succeeded in proving that 99 out of 100 children from Benin and Togo had aflatoxin in their blood," Professor Richard Sikora of the Bonn Institute of Plant Diseases explains. "The consequence is drastic impairment of growth and of other types of development."

'Good' mould displaces its highly toxic cousin

The remedy may lie in the idea of US researchers Dr. Peter J. Cotty, which is both simple and ingenious. "In addition to the dangerous strain aspergillus flavus there are also others which cannot produce any toxin," the Bonn plant pathologist Dr. Sebastian Kiewnick explains. "Cotty propagated this non-toxic strain of aspergillus on grains of corn and spread the mould-infected grains in fields of cotton. As a result, the non-toxic strain was present in substantially larger amounts and was thus able to almost entirely supplant the toxic variety." The success was overwhelming: aflatoxin infection of the cotton cobs dropped from an average of 1,000 ppb (parts per billion) to below 20 ppb, thereby lying within the US safety limit for animal food – cotton seeds serve as food e.g. for dairy cattle.

Two years ago the 'good' mould was permitted in the US as an organic pesticide. Five kilos of mould-infected grains of corn are sufficient to 'inoculate' an area of one hectare – this means that the method is relatively inexpensive. "For developing countries, particularly, this would be the ideal strategy to get the upper hand of the aflatoxin problem," Professor Sikora thinks.

He has had quite a lot of experience with combating tropical plant diseases. For two years the Bonn team, together with colleagues from the IITA in Benin and Nigeria, have been looking for a mould isolate which is guaranteed to be unable to produce aflatoxin – after all, they do not want to fight Satan with Beelzebub. "Apart from that the aspergillus variant has to be so sturdy that it can assert itself against its toxic cousin in the wild," Professor Sikora says.

Promising strains among 3,000 isolates

The Federal Ministry of Economic Co-operation and Development (the BMZ) is supporting the project until 2006 to the tune of a total of 1.2 million euros. The researchers have made an important advance: "We have examined 3,000 isolates in all and have come across several promising strains," Sebastian Kiewnick states. "Now we'll soon be conducting the first field trials." Should they be successful, the team want to develop a quick and easy method for propagating the non-toxic mould for use en masse.

There is no danger of additional damage as a result of 'inoculating' the fields with mould, it is claimed. "It can scarcely be prevented that maize or nuts will be infected to a certain extent with brown mould," Sebastian Kiewnick emphasises. "We can only influence which strain of aspergillus grows on it: a dangerous producer of toxins – or the non-toxic variant."

Source : University of Bonn