Luck of the draw for salty genes

Australian researchers have discovered two new genes from an ancient wheat variety that promise to improve salt tolerance in both durum and bread wheat.

The two genes, Nax1 and Nax2, work by excluding salt from different parts of the plant, one from the roots and the other from the leaves. And it was a bit of luck that led the team to the discovery.

"The two genes originally came from a wheat ancestor, Triticum monococcum," the research team leader, CSIRO Plant Industry's Dr Rana Munns, said. "They were brought in accidentally in some durum wheat 35 years ago by a wheat breeder who was looking for other genes but they just happened to be linked to the ones that we later on were looking for. It was one of those fortunate accidents."

The team was hoping to identify wheat varieties that could cope with higher salinity and were particularly interested in the premium-priced durum wheat, which is much more salt-sensitive than bread wheat.

They used a more precise version of atomic absorption spectrophotometry, the standard screening process for measuring elements in plants. The new technique, inductively coupled plasma or ICP, involves converting the liquid sample into a plasma, or ionised atoms. Chemical elements emit light in characteristic wavelengths when put into a highly energised state, so the sodium levels in the team's samples were able to be measured.

"We screened a hundred durum wheats from the Australian Winter Cereals Collection at Tamworth, which contains tens of thousands of wheat types," Munns said. "Highlighting the fact that the science of plant breeding sometimes relies on an element of good fortune, we were lucky to find the durum variety with the ancient genes straight away, otherwise we might have been looking for years."

The team then constructed molecular markers, which are now in use in CSIRO's wheat breeding program. A durum wheat variety as salt-tolerant as bread wheat is in advanced field trials and could be commercially available in three years.

Munns said durum wheat was a particular target as it is used to make pasta products, which have a higher value than bread.

"We've started crossing the genes into bread wheat," she said. "Bread wheat does have some salt tolerance but it's a slightly different mechanism. We are planning to add the durum mechanism into the bread wheat mechanism.

"We have preliminary results that show we have increased the ability of the bread wheat to keep the salt out, but we still have to test it in the field. Bread wheat is quite tolerant to salt, but we think it too can be improved. Our aim is to eventually produce wheats able, like barley, to grow in highly saline soils."

Interest has already been generated in California, which grows durum wheat and has soil salinity problems, as does France and Italy, she said. "India, Pakistan, China - they've all got major salinity problems like we do."

The research is a collaborative project between CSIRO, the NSW Department of Primary Industries, the University of Adelaide and the Australian Centre for Plant Functional Genomics, with support from the Grains Research and Development Corporation (GRDC) and the CRC for Plant-based Management of Dryland Salinity.

Papers outlining the work have been published in the journal Plant Physiology (December 2006, Vol. 142, www.plantphysiol.org) The discovery of the two genes is the subject of international patents.