Enhanced volatile emission in Zea mays as a powerful tool to fight insect root pests

1602-3952-LI-ZE

Background

Of all grain cultivated, maize is the most important one with a worldwide production of approxi-mately 774million tonnes in 2007/2008 and annual growth rates up to 10%. Not only is maize staple food in many regions of the world, it is also a major source of starch for the chemical in-dustry and increasingly used as biomass fuel and feedstock for biogas plants. Hence, protection of the crop against herbivores is pivotal to meet the growing demand.

The Western Corn Rootworm (WCR) is the most severe pest in maize in the United States, where it causes annual damage up to 1 billion dollars. In Europe it is rapidly spreading from the Balkan region to other countries, giving rise to the assumption that the present annual losses of about 300 million euros will soon be exceeded. Extinction of the WCR is difficult, since pesti-cides are expensive and rather ineffective, whereas the use of maize lines genetically modified to produce toxins able to kill the pest gave rise to the formation of resistant WCR strains.

Interestingly, it has long been known that plants are able to produce volatiles that attract natural enemies of their respective herbivores.¹ In case of Zea mays, the roots release a sesquiterpene in response to WCR larvae. The organic compound then attracts entomopathogenic nematodes (EPN) that are able to parasitize and kill the herbivore. On the other hand, field studies showed that North American maize lines lack the ability to release the volatile, which highly increases their susceptibility for pest infestation.²

Technology

Scientists from the Max Planck Institute for Chemical Ecology in Jena together with scientists from the University Neuchatel (Switzerland) have jointly overcome several obstacles in re-establishing emission of the volatile and in turn nematode attraction by transforming US-maize with a uniquely suited sesquiterpene synthase (see their original publication³).

Field data show a significant decrease in root damage of transformed plants that constitutively express sesquiterpene when compared to control cells. Furthermore, less adult WCR beetles were detected near transformed plants. Taken together these results indicate that plant volatile emissions can be manipulated to enhance the effectiveness of biological control agents. Our genetically modified plants therefore open the way for novel and ecological strategies to fight insect pests.

	Figure 1 Average root damage upon EPN treatment is lower in transformed plants Upon exposition to both, WCR (Western Corn Root-worm) eggs and EPN (entomopathogenic nematodes), roots from transformed plants had significantly less damage than roots from control lines.
	Figure 2 Mean number of emerging adult WCR bee-tles near transformed, emitting plants decreased significantly when EPN were applied Significantly fewer adults emerged near sesquiterpene producing transformed plants than near transformed plants that were not emitting the volatile.