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Technology Spurs Alfalfa Genome MappingBy Jan Suszkiw
August 2, 1999
Using computer technology to magnify light microscope images, scientists are getting the closest look yet at the chromosome housing for alfalfas genes.
The advance opens the door to genome mapping of alfalfas 32 chromosomes for traits like winter hardiness, stand persistence, and resistance to pests like potato leaf hoppers.
Alfalfa is among Americas 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, alfalfas 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 legumes 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, USDAs 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 months issue of Agricultural Research, an ARS publication also on the Web at: