The path to sugar rich beet
with improved seedling vigour, higher sugar content, and enhanced
disease resistance.
J. Mitchell McGrath, a geneticist at the Agricultural Research Service (ARS) Sugar Beet and Bean research unit in the US, and his team have developed a simple test for seedling emergence. The emergence test has already led to commercial varieties with higher germination rates, claim the researchers.
The team also discovered two possible genetic markers for seedlingvigour, which is the ability of a seed to sprout and of the seedling tosurvive in adverse environments.
With regards to high sugar content, the researchers found a possible marker to predict beets with this trait when they are about seven weeks old, instead of waiting for full growth in 25 weeks.
McGrath and colleagues theorise that beets with the highest sugar content are notbetter at storing sugar, just better at keeping the concentration highby letting less water in.
McGrath began with sugar beet DNA he prepared and worked with a contract firm to prepare and package a library. Each clone in the library of 38,400 cloned bacteria stores a different DNA sequence from the beet's genome.
"We chop up sugar beet DNA and connect segments to bacterial plasmids that carry the DNA into E. coli bacteria," McGrath says. Seed companies can then either buy cloned copies of the living bacterial library or DNA samples on filters or they can rely on McGrath or the contract firm to compare their germplasm's DNA sequences with those in the library to identify traits-or at least chromosome location-associated with each DNA sequence.
"This is an important first step to create order in these early days of sugar beet genome mapping," said McGrath. "We don't have a common language for any of the beet's nine chromosomes."
The scientists are also on the trail of the genes for resistance to twomajor seedling disease agents: aphanomyces and rhizoctonia. Disease is the main threat to a seedling's survival in its first month. Theresearchers have developed a test for Aphanomyces seedling disease and used it to show there are two genes for resistance.
The European Union, Brazil, Cuba, Thailand and Australia dominate sugar export trade. The major sugar importers include China, Russia, the USA, Canada and Japan.
World sugar consumption has grown steadily by around two per cent each year in recent years and the annual global sugar consumption is currently about 130 million tonnes.
