Technology Spurs Alfalfa Genome Mapping

Using computer technology to magnify light microscope images, scientists are getting the closest look yet at the chromosome housing for alfalfa’s genes.

The advance opens the door to genome mapping of alfalfa’s 32 chromosomes for traits like winter hardiness, stand persistence, and resistance to pests like potato leaf hoppers.

Alfalfa is among America’s most widely grown crops, generating over $6 billion annually, primarily as hay. Yet compared to corn or soybeans, less is known about its complex genetic make-up, slowing breeding efforts. Over the past 30 years, for example, alfalfa’s average yield has only increased by about one percent.

Part of the problem also stems from the fact that alfalfa plants are autotetraploid, meaning their traits are governed by genes residing on four chromosomes instead of two. The legume’s chromosomes are also hard to distinguish, and barely visible under a microscope.

Or so it was until scientists Gary Bauchan and Azhar Hossain tackled the problem. With help from a Maryland firm, Loats Associates, they attached a light microscope to a computer imaging system at their Beltsville, Md., Soybean and Alfalfa Research Lab, operated by the Agricultural Research Service, USDA’s chief scientific agency.

The result: a 10,000-fold increase in magnification, use of false-color, and the precise identification and measurement of the chromosomes’ length--key to karyotyping, or arranging them from largest to smallest.

Along the chromosomes’ “arms,” scientists observed thick bands of heterochromatin, material composed of DNA and protein. Like chromosomal roadblocks, the bands can impede the exchange of genes during breeding. One hope is that falcata alfalfas, which contain relatively few heterochromatin bands, will help breeders introduce new traits from wild species to domestic cultivars, broadening their genetic base.

A longer story about the advance appears in this month’s issue of “Agricultural Research,” an ARS publication also on the Web at:

/is/AR/archive/aug99/gene0899.htm

Scientific contact: Gary Bauchan, ARS Soybean and Alfalfa Research Laboratory, Beltsville, Md., phone (301) 504-6649, fax (301) 504-5169, gbauchan@asrr.arsusda.gov.