Barley lines that can tolerate the yield-depleting toxic effects of high soil-boron levels will be field-trialed in SA next season.
Boron toxicity is estimated to cause yield losses of up to 17 per cent and is widespread in SA, Victoria and parts of WA.
While an essential nutrient in small doses, in high doses "boron-toxic subsoil acts as a barrier to root growth, restricting access to valuable subsoil moisture and nutrients. The toxicity shows as brown spots which form initially at the leaf margins and later extend over the entire leaf," said barley breeder Steve Jefferies, with the SA Barley Improvement Program.
"In severe cases, the brown spots can appear on leaf sheaths, stems, ears and awns."
He said a number of current wheat varieties including Frame and Krichauff are moderately tolerant to boron toxicity. They have succeeded Halberd, Spear and Dagger, which dominated sowings for many years — in part due to their moderate tolerance to boron toxicity. Other common barley varieties are very intolerant of boron toxicity.
Mr Jefferies said barleys from many parts of the world were investigated for their boron tolerance, and Sahara from North Africa emerged as the best. However, it was poorly adapted to modern farming systems and so the boron tolerance in it had to be transferred to high-yielding Australian cultivars.
The researchers recruited the tools of DNA technology to speed their breeding work.
Mr Jefferies and his colleagues identified the location of four genes that control boron tolerance in barley plants. The experimental lines came from a cross of the boron-intolerant Clipper variety with Sahara. Molecular markers (DNA fingerprints) for the genes were identified for three of the four chromosome locations.
"We can now determine if a plant is boron-tolerant by looking for the specific DNA fingerprints in a small piece of leaf tissue. This can take less than a week compared to one or two years of field and laboratory testing.
"Using these methods we are well advanced in introducing boron tolerance into Sloop by crossing Sloop with Sahara, and we expect to have these lines in field trials in 1999."
Victorian barley breeder David Moody is also using the molecular markers to identify boron-tolerant lines in the Victorian program.
Mr Moody said the program is taking precautions not to compromise Sloop's good malting qualities by crossing it with Sahara, and the ability to select for only the boron-tolerance traits is a big help.
The research is a collaborative project involving the National Barley Molecular Marker Program, the Cooperative Research Centre for Molecular Plant Breeding and the GRDC southern region barley improvement programs.
Program 1.7.2 Contact: Mr Steve Jefferies 08 8303 6531
(far left) On the right in a boron-toxic soil, the boron-tolerant Sahara, and elsewhere intolerant varieties including Clipper, Mundah and Schooner, (left) The graphic differences in root growth between the boron-tolerant Sahara and the intolerant Clipper.