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Disease-resistant genes could bring greater crop yields

By Stewart MacInnis

Spectrum Volume 19 Issue 11 - November 7, 1996

Scientists have another weapon to fight diseases that cause billions of dollars in crop damages world-wide, thanks to a technique developed by scientists at Virginia Tech.

The success of the biotechnology technique for identifying the genes that confer disease resistance in plants is published in the current issue of the Proceedings of the National Academy of Sciences. Virginia Tech researchers M.A. Saghai Maroof and Glenn R. Buss co-authored the paper with former Virginia Tech scientist Yong G. Yu, now a researcher for Union Camp Corporation in Princeton, N.J.

The team was able to build on work done by other researchers, who succeeded in isolating the genes controlling disease resistance in tobacco and in mustard weed. The key step forward made by the Virginia Tech researchers was in developing a technique to use DNA sequences common to the resistance genes in those two crops to identify the similar genes in soybeans.

That knowledge will allow scientists to target genetic-engineering and selective breeding efforts to develop the disease-resistant soybean varieties. The technique also holds promise to find disease-resistance genes in other crops.

"Without this technology, to find a specific gene is like looking for a needle in a haystack," said Saghai Maroof, a professor in the Department of Crop and Soil Environmental Sciences and director of the research project. "This approach should facilitate cloning of disease-resistance genes in soybean and other crops, and this finding should have wider biological implications."

With about 30,000 genes containing all the genetic information that makes a plant a soybean and yet also makes it an individual, finding a specific gene that confers resistance to certain a disease is a laborious task.

An aspect of Saghai Maroof's research project since joining Virginia Tech in 1989 has been the application of molecular marker technology--commonly referred to as DNA fingerprinting--to the identification and isolation of genes controlling resistance in several crops. The technique developed at Virginia Tech uses that technology in conjunction with genome mapping to create a strategy to target researchers' efforts.

Genome mapping is the identification of the genes, their locations on the chromosomes, and the traits they determine. Though scientists in many countries are working on genome mapping, only a small fraction of the vast array of species in the world is being studied, and only in a few species has a genome map been completed. For most species, only a small portion of the genome has been mapped.

Being able to exploit the information developed by scientists working on one species to find a specific gene in another species is a powerful tool for researchers, according to Saghai Maroof. It has the potential to eliminate years of tedious work.

Buss, who has been working with Virginia Tech scientists Curt Roane and Sue Tolin on soybean virus diseases for 20 years, notes that world-wide crop losses amount to billions of dollars each year. The loss to soybeans due to diseases in the U.S. Sunbelt alone amounted to $266 million in 1994, according to official estimates.

"The most economical and environmentally friendly approach to control losses due to diseases is the development of resistant cultivars," Buss said.

Dollar figures describing the potential savings such technologies could bring are easy to understand. Not so easy to grasp are the potential human savings. Forty thousand children die each day from hunger and hunger-related illnesses. An estimated 800 million people around the globe are malnourished. The number of mouths to feed world-wide increases by 90 million each year.

Further progress on the soybean disease research is expected from the Virginia Tech team with new funding from the U.S. Department of Agriculture-National Research Institute competitive grants program, says Jack Hall, head of the Department of Crop and Soil Environmental Sciences. The team is now collaborating with scientists from Iowa State University on the application of biotechnology to combat soybean diseases. That project is funded by the National Soybean Board.