Fungi don't like Bt

May 2012

Corn harvest in Minnesota, USA. Photo by PXLated on Flickr

A major focus for GM crop development has been in 'Bt' crops which generate their own insecticides modeled on similar proteins produced by Bacillus thuringiensis soil bacteria.

Because Bt-protein has been passed off as highly specific in its ability to kill certain insect pests, it has been assumed safe for the wider environment. However, no one's actually been testing this assumption.

In the US in 2011, 88% of the corn cultivated was GM. Most of it was transformed to express a Bt insecticide. Globally, GM corn is grown in at least 16 different countries. Shocking therefore, to realise that scientists have only just begun to look at what Bt crops do to the soil. And, not surprisingly, when scientists began to look, they found problems.

Soil fungi are a vital component of healthy soil and the whole soil ecosystems, including the plants growing there.

Some fungi have a symbiotic relationship with corn: the fungus grows intimately with the corn roots, increasing the size of the root system and making more nutrients and water available to the plant; in return, the fungus is supplied with sugars and proteins made by the plants.

When scientists measured how many fungal connections were present in the roots of several types of Bt corn compared with equivalent conventional corn in the same soil under greenhouse conditions, they found that the bonds were decreased in the GM roots. The scientists found no evidence that any Bt protein was directly toxic to the fungi nor that it had any short-term detrimental effect on subsequent crops in the same soil. They also established that there was no reduction in the size of the corn's shoot or root system as an immediate effect of the reduced fungal relationship.

The next stage in the experiment will be to see what happens in the field, and what happens to the soil after successive Bt crops have been growing in the same ground for multiple years as is now common practice in agriculture.

OUR COMMENT

In the field, the effects of reduced fungal symbionts could become very marked: the plants will be subject to environmental stresses stacked on top of impaired nutrient availability. It could well be that there is yield loss, or that the Bt crops become more susceptible to secondary pests (this has already been observed), or that greater levels of artificial fertilizers need to be applied: all of these scenarios mean increased production costs for the farmer and the end-user (you).

The most concerning aspect of this experiment is that every one of the different strains of Bt corn tested showed an inhibition of fungal connections. Are the fungi sensing something un-corn-like in these GM plant roots with bacterial proteins coming out of them? If this seems too intelligent an act for a fungus, ready TADPOLE TAILS AND ROUNDUP HERBICIDE - April 2012: the inappropriate reaction tadpoles have to the presence of Roundup herbicide is one they evolved to deal with predators in their environment.

SOURCES

• Genetically modified corn affects its symbiotic relationship with non=target soil organisms, http://phys.org/news/2012-04-genetically-corn-affects-symbiotic-relationship.html, American Journal of Botany 99(4)
• Ryan Villarreal, Monsanto Bt Crops Genetically Modified Corn linked To Soil Ecosystem Threat, www.ibtimes.com, 17.04.12