September 14, 2009

A natural method for limiting soy aphids could be another weapon for farmers battling the destructive insect.

 

The soy aphid has menaced farmers since its arrival in the US in 2000 and can cause yield losses as high as 40 percent, but researchers at the University of Illinois have developed a soy seed with natural resistance to the bug.

 

The seeds are not considered genetically modified because they use the soy's own genetics, but these seeds have been bred to amplify that particular trait, called Rag 1 antibiosis. The researchers created two types, a conventional seed that organic farmers can use and one that includes glyphosate, the herbicide commonly known as "Round Up."

 

The aphid resistant gene in the soy seeds does not eliminate aphids, but crops with the resistance had significantly less aphid populations than fields with non-resistant crops, said Matthew O' Neal, assistant professor and soy entomologist at Iowa State University.

 

Aphids can multiply rapidly, but the Rag 1 gene can slow the reproductive growth of the bugs and help keep populations below threshold levels that will produce significant yield losses. Soy are most susceptible to damage from aphids when they are in the R1 to R5 stages of development, which is from when the crop first flowers to when the soy pods are about 1/8 inch big. Beyond that, they can tolerate aphids.

 

"My hypothesis is the seeds will slow aphid growth, delaying the expansion of their populations in fields to the crop's threshold levels until it is far enough along to withstand the impact on yields," said O' Neal.

 

Aphids feed on the sap in plants, damaging the photosynthesis process, and they secrete honey dew that opens the door for mould and fungus to grow. In addition, they can transmit viruses from plant to plant.

 

The aphids can transmit viruses like humans who share dirty hyperemic needles, passing along diseases to everyone that uses them, O' Neal said.

 

If the seeds are successful, it will limit the use of insecticides that will save producers money as well as help limit chemicals reaching into water supplies.

 

"If farmers can deploy resistance through the genes in seeds, this could reduce the use of these insecticides, which will have many environmental benefits," said Brian Diers, professor of soy breeding at University of Illinois.

 

The test on the seeds at U of I shows the resistance reduces the number aphid reproduction. In U of I field plots 50 percent reductions in aphids were observed, Diers said.

 

"There is currently a limited amount of the commercial aphid resistance seeds available this year, but Syngenta hopes to release a variety next year in the US after licensing the technology from U of I," said Diers.

 

Pioneer and Monsanto Co. are working on this technology as well, Diers said.

 

Economics will play a key role in the use of the seeds, as farmers will have to weigh the costs of using the seeds. On average it costs in the range of US$8 to US$16 an acre to spray for aphids, and so how the seeds are priced will go a long way for their expanded use, O' Neal said.