Agricultural Research Service scientists, in Ames, IA, have cloned and characterized the powdery mildew resistance gene from barley.

This is the first successful cloning of a gene that confers active disease defense to small-grain cereals.

ARS geneticist Roger Wise, post-doctoral assistant Dennis Halterman and PhD candidate Fusheng Wei, at the ARS Corn Insects and Crop Genetics Research facility, in Ames, collaborated with Paul Schulze-Lefert's group, at the Sainsburg Laboratory, in the United Kingdom, to isolate from barley two of the 30 alternative forms of the Mla resistance gene, Mla6 and Mla1. A patent has been filed on the newly isolated genes.

Powdery mildews form a superficial white, powdery coating on leaves, buds, shoots and flower petals. The mildews are caused by more than 1,600 species of fungi.

Fungal pathogens are perhaps the greatest impediment to cereal grain production worldwide, sometimes causing yield losses of up to 50%. To reduce such losses, plant breeders have turned to genetic varieties that resist fungal diseases.

In recent years, scientists have successfully cloned resistance genes from a variety of model plant species, such as Arabidopsis, rice and tomato. The Arabidopsis genome--120 million letters of genetic code--is the smallest in plants. It has been more difficult to isolate genes from crop plants, some of which possess genomes even larger than that of human beings. For example, the barley genome is 40 times larger than the Arabidopsis genome.

The Ames researchers were able to show that Mla6 confers resistance to powdery mildew in wheat. This is the first demonstration of using genetic engineering to transfer a resistance gene between cereal crop species.

The research aids the understanding of how disease resistance genes work in interactions between pathogens and their crop plant hosts.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

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