Developing Super Plants

Probably since plants were first cultivated, people have wished for ways to build the perfect specimen – a super-plant that resists most diseases and insects and produces the highest quality crop with fewest resources. The traditional way to create super-plant varieties is through selective breeding, a process pioneered by Gregor Mendel in the 1850s. Selective breeding involves breeding together two plants that have desired traits to produce offspring with the desired qualities of both plants. But this process is time-consuming and inexact. Successful new crop varieties are the result of a wait-and-see strategy that takes several generations and many years to accomplish.

Enter the age of genetics and new high-technology tools that speed things up. When two plants are bred together, geneticists use gene mapping to distinguish whether a desired trait was passed on by looking directly at the DNA of the offspring. Gene mapping is the science of examining the chromosomes of a given organism to find the location of a gene or genes that control a certain trait.

"We follow pieces of DNA on a gel to make a map that is representative of the genes in an organism," says Nora Lapitan, associate professor in the Department of Soil and Crop Sciences at Colorado State University. The tricky part is that even simple plants have tens of thousands of genes, and only small sections of DNA can be examined at one time. To make things easier, geneticists look for visual clues or DNA markers that help them figure out where they are on the DNA strand and which genes they are looking at. "DNA markers are like landmarks on the gene map," Lapitan says.

The Colorado State researcher has used gene mapping since 1989 to produce knowledge that helps plant breeders improve wheat, potato, and barley crops.

For more than a decade, Colorado's multi-million dollar wheat industry has been the target of a tiny, destructive insect called the Russian wheat aphid. Chemical control is costly and may be environmentally threatening. Lapitan worked on the problem with colleague Jim Quick, who identified several wheat genes that allow the plant to generate a natural resistance to the aphid. Lapitan then was able to provide wheat breeding programs with the DNA markers for two of these genes.

"This speeds the process for breeders who want to add natural aphid resistance as they develop new varieties," says Lapitan. "Because they know what to look for, wheat breeders are able to produce desired results much faster than with conventional breeding programs."

Lapitan and colleague Carol Ishimaru used a similar genetic approach to control bacterial ring rot, a common bacterial disease in potatoes. Because the pathogen of this disease often is latent, it will show up in some generations and skip others, making it extremely difficult to work with using traditional selective breeding programs. Though they haven't been able to identify a genetic code for total immunity, Lapitan and Ishimaru have been able to identify markers for several genes that show high levels of resistance.

Another challenge to build a super-plant came from the barley industry. A fungus disease called fusarium head blight, or scab disease, severely curtails production of malting barley, the main feedstock of the beer-brewing industry. This project is national in scope; North Dakota State University and the University of Minnesota do field work while Lapitan and her team at Colorado State handle the laboratory work. Funding is from the U.S. Department of Agriculture, the brewing industry, and the American Malting Barley Industry.

Even though the genetics of barley scab resistance are more complex than for Russian wheat aphid, Lapitan says four chromosome regions have been identified that show promise for genetic resistance to barley scab disease. Further studies are underway.

For all the direct practical application of her research, Lapitan remains modest. "All we're doing through gene-mapping and DNA marking is speeding up the process of identifying and combining genes that produce desired traits in plants. That's what plant breeders have done for hundreds of years through conventional plant breeding."