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Resistant corn hybrid patented

Spectrum Volume 19 Issue 13 - November 21, 1996

Virginia Tech and Garst Seed Company, based in Slater, Iowa, have announced that a patent has been jointly granted to create corn hybrids with built-in resistance to gray leaf spot (GLS). This patented process results in the transfer of genes from corn plants with a naturally high resistance to the disease into elite, high-yielding hybrids.

The process, a result of collaborated research conducted at Virginia Tech, allows Garst to produce hybrids with high levels of resistance to gray leaf spot, a fungal disease that attacks corn and reduces yield.

Before this gene-transfer process was discovered, corn hybrids were conventionally bred to possess tolerance to the disease, but these new hybrids will be the first with this type of built-in protection, said Erik Stromberg, Extension plant pathologist at Virginia Tech. Resistant hybrids are defined as having the ability to overcome pathogen activity and disease by suppression or prevention.

"The development of this process began with a corn-hybrid line developed by Virginia Tech that showed extremely strong resistance to GLS," Stromberg said. "By extracting just the DNA that determines the GLS-resistance trait and leaving all other genetic material behind, scientists at Garst were able to put the basic genetic-resistance profile of this plant into high-yielding hybrids."

Using molecular biotechnology techniques, such as "fingerprinting," Garst scientists were able to develop a picture of where genes are located that work together to account for unique traits such as GLS-resistance. Complicated traits, such as yield, require many genes interacting with each other, causing different reactions, according to Al Balducchi, plant pathologist, leader for the Garst GLS project team.

"Fingerprinting dramatically reduced the time it typically would have taken for field testing at each level to see which traits were expressed. Using this process, field testing could wait until the hybrid was near commercialization," Stromberg said.

"These GLS-resistant hybrids have shown to be good performers, with or without the disease present," says Balducchi. "The hybrids do this by keeping more green leaf tissue during the grain-filling period even when under attack by GLS, therefore maintaining their yield potential."

According to reports from Midwestern universities, GLS is spreading 50 to 100 miles north every year, from a base that was historically only the Ohio River bottoms, Balducchi said.

It would not be unusual to see up to a 40-percent drop in yield potential in a field hit hard by GLS, Stromberg said. Other economic losses could be through poor test weights, premature plant death, and slower-than-normal drydown.

Although not as severe as in 1995, when the disease caused severe to light damage in 23 million acres, several corn-growing areas were hit by GLS this year, including fields in Iowa, Illinois, Indiana, Ohio, Kentucky, and Tennessee. For the first time, GLS outbreaks were reported in several southern and central counties in Nebraska. Many popular hybrids proved extremely susceptible to the disease.

Buying protection against the disease in seed is more economical and convenient for growers than a fungicide treatment, Stromberg said.