Wheat Losses to Leaf Blotch Stemmed by Resistant Gene

WEST LAFAYETTE, Indiana, August 20, 2003 (ENS) - A gene in bread wheat plants that is resistant to an economically crippling leaf blotch fungus has been discovered by a research team working at Purdue University. The fungus causes wheat crop damage worldwide with yield losses of 50 percent or even more in some places.

In the United States the leaf blotch is widespread in the Pacific Northwest, the northern Great Plains and the eastern Midwest soft wheat region, and experts estimate annual losses at $275 million.

News of this discovery was immediately felt on the sensitive wheat futures market. Commodities grain trader Hugh Bellingreri with Wentworth Bell told ENS that this morning wheat futures on the Chicago Board of Trade began to sell off sharply as fund managers learned of the scientific development.

December '03 wheat futures on the Chicago Board of Trade took the biggest hit on the news. Prices slid 12.5 cents during the day after a strong opening, closing at 3.78 3/4 cents per bushel. The wheat price moved lower because of the potential for increased future wheat supplies as a result of this newly found gene, Bellingreri explained.

The wheat farmers' enemy is the fungus Mycosphaerella graminicola, the sexual state of Septoria tritici, that causes leaf blotch in wheat. Leaf blotch does not kill wheat plants, but it weakens them enough to cause major crop losses.

The resistant gene and its markers are naturally occurring in wheat lines already in use, so they can be used immediately for farmers' breeding programs to gain protection against leaf blotch, said lead scientist Stephen Goodwin, associate professor of botany and plant pathology at Purdue and a scientist with the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), which funded the study.


Stephen Goodwin, associate professor of botany and plant pathology at Purdue University (Photo by Tom Campbell courtesy Purdue University)
The Purdue team used the bread wheat species to find the pathogen resistance gene and the markers, or bits of DNA, that indicate the presence of the naturally occurring gene.

As soon as a seedling sprouts, a small piece of the young leaf can be ground and then a DNA test can be run. This shows whether the resistance markers are present.

"The goal of our work is to find additional resistance genes to the fungus Mycosphaerella graminicola so we can use the lines carrying these genes in our wheat to avoid the breakdown of resistance in the plants," said Goodwin.

"Having the markers greatly speeds up the breeding process for resistant plants. Using the markers, in a few days you can tell which plants have the resistance gene and which don't," Goodwin said.

The other researchers involved in this study are Tika Adhikari, USDA-ARS and Department of Botany and Plant Pathology postdoctoral fellow, and Joseph Anderson, USDA-ARS scientist and Purdue Department of Agronomy assistant professor.

The team discovered the gene Stb8, so named because it is the eighth gene known to provide resistance to Septoria tritici leaf blotch (STB).

Several of the previously found genes conferred resistance on bread wheat plants for up to 15 years. But Stb8 has genetic characteristics that may allow it to be effective for a much longer period of time, Goodwin said.


Septoria leaf blotch of wheat (Photo courtesy Alberta Agriculture, Food and Rural Development)
The genome containing Stb8 originated from a pasta wheat parent, which is resistant to most strains of the fungus. This may extend the usefulness of the resistance gene for bread wheat.

The specific location of Stb8 on the genome is different than all the previously known resistance genes for wheat blotch. This site should allow Stb8 to be combined with other genes that also offer some protection against the disease, thereby increasing plants' resistance.

"If we can understand these biochemical processes that lead to resistance, then in the future we may learn how to modify them to make these genes more durable," Goodwin said.

Though different resistance genes seem to work more effectively in different parts of the world, the pathogen is easily spread, especially with rapid worldwide transportation. The fungus is spread and grows by spores, and it can survive in dried leaves for a long time, Goodwin said.

"We even store them that way, sometimes for years," he said. "If you keep the leaf dry, it won't decay and the pathogen just sits there. Or you can freeze it at 80 C, thaw it, and then spray it with water. It will start growing."

Purdue scientists determined resistance to the fungus by observing whether the disease appeared on the leaves of adult plants and by measuring the number of spores present.

Goodwin said the long term goal of the research into the characteristics of leaf blotch resistance genes is to learn about the molecular pathways that allow the plants to respond to pathogens.

Results of the Purdue study on resistance to the fungus that causes Septoria tritici leaf blotch are published in the September issue of "Phytopathology" and appear on the journal's website at: http://www.apsnet.org/phyto/current/top.asp