Science Update

Avian Flu: A Weak Strain Takes Deadly Shape

In 1983, more than 17 million chickens were slaughtered to halt an outbreak of highly pathogenic avian influenza (AI) virus in the United States. Now ARS scientists have shown that the surface of the AI virus mutates rapidly—and continually—much like human flu viruses. The discovery supplies a potential new tool for predicting which AI strains are likely to become highly pathogenic. Such a strain began killing Mexican poultry late last year. ARS researchers studied several isolates of AI from Mexico. They found that weak strains turned deadly during continual rapid mutation of a certain gene. This gene controls structure of a molecule called hemagglutinin (HA).

Hundreds of arm-like HA molecules project from the membrane envelope of a single AI particle. The virus uses HA to dock with and dispense its genes through cell membranes in a live chicken or other bird. Viral genes then commandeer the cell machinery. HA molecules of weak AI strains bind and merge only with respiratory tract or gut cells. But when HA mutates rapidly, odds increase that a less discriminating strain will emerge. The deadliest strains are those that can bind to and grow in cells of other organs of the bird, especially the brain and heart. The computer-generated diagram [at right] depicts an HA molecule. Red areas are sites where mutations occurred during emergence of the lethal Mexican strain.

David E. Swayne, USDA-ARS Southeast Poultry Research Laboratory, Athens, Georgia; phone (706) 546-3432.

New Bean Rots Not

U.S. growers of certified seed can now get Probst soybean, a new high-yielding, disease-resistant variety. The variety was developed in the cooperative soybean breeding and genetics project of ARS and Purdue University. In 46 field tests in 1992 and 1993, Probst had the highest 2-year average yield of five publicly developed varieties and five advanced breeding lines. It resists many races of Phytophthora sojae, a root-rot fungus that robs crop yield. Albert H. Probst was an ARS soybean breeder from 1936 to 1970.

USDA-ARS Crop Production and Pest Control Research Unit, 915 West State Street, West Lafayette, Indiana; phone (765) 494-6076.

U.S. Holsteins Still World Champs in Gene Competition

U.S. Holsteins remain the world's No. 1 genetic source for top milk production, according to a recent ARS study. Researchers evaluated the genetics of bulls from the United States, Australia, Canada, Denmark, France, Germany, Italy, The Netherlands, New Zealand, and the United Kingdom. They did this by comparing production of milk, fat, and protein from the bulls' daughters. This revealed that 60 to 80 of the top 100 bulls for each trait were from the United States. Continued U.S. improvements are essential, though. Otherwise, foreign use of U.S. genetics could eventually close the nation's competitive advantage. Already, other countries' top bulls consist of half, three-quarters, or even full "U.S. genetics."

Rex L. Powell, USDA-ARS Animal Improvement Programs Laboratory, Beltsville, Maryland; phone (301) 504-8174.

Y Not? — Virus-Resistant Biotech Potato Has Wild Genes

A new potato hybrid could save growers millions of dollars in the fight against potato virus Y (PVY). The best defense farmers have today comes from planting certified virus-free seed potatoes. But screening seed potatoes is costly and time-consuming. ARS researchers developed the new hybrid as a promising alternative. It gets its PVY resistance from a wild South American species, Solanum etuberosum. Researchers used biotechnology methods to fuse its leaf cells with those of domesticated potato plants and to regenerate whole-plant hybrids. They resisted the virus, and so did offspring produced with sexual crosses using the hybrid.

USDA-ARS Vegetable Crops Research Unit, Madison, Wisconsin; phone (608) 262-1248.

"Science Update" was published in the July 1995 issue of Agricultural Research magazine.