How science can help get farmers through the big dry

One of Australia's recurring agricultural problems is drought, and this year is no exception, with widespread drought conditions across many of Australia's prime agricultural regions.

So it's not surprising to discover that developing drought-tolerant crops is a major target for breeders and agricultural biotechnologists around Australia.

"Almost all commercially grown wheats in Australia were derived from a Mexican-bred strain developed for wet fertile soils," said CSIRO wheat researcher Dr Richard Richards.

In addition, these varieties have a dwarfing gene that has a negative impact on growth in the arid Australian conditions, as the primary shoot is smaller than usual, and has problems puncturing up through the stubbly soil. But dwarf varieties are desirable for their higher yields and reduced resource needs.

So CSIRO scientists have identified the genes responsible for dwarfing traits in wheat, and in the process learned how to uncouple the primary shoot size from the eventual height of the plant.

"It's working very, very nicely. In fact, this uncoupling has been not only important in producing a longer primary shoot, but it also releases more energy from the plant. The older dwarfing genes act as a brake on the early growth of the plant," Richards said.

"We finish up with wheat with the desirable short height, but not the negative features."

This approach has been incorporated into a number of varieties in development by CSIRO, using molecular marker technology to assist with the breeding process, and some of these strains are in field trials for the first time this year, said Richards. He noted that it would be a couple of years before commercial decisions on the new varieties were made, but expected that growers would welcome the new strains.

However, this is not the only approach being taken by CSIRO wheat breeders. In addition to this variety, there are several other avenues of investigation.

For example, while the new Drysdale strain was developed using conventional rather than biotechnology techniques, the researchers are looking for the genes involved in the process. They are also investigating genes that result in increased vigour and better carbohydrate storage in the grain.

Richards explained the reasoning behind looking at carbohydrate storage. Most carbohydrates in wheat grain (which is 85-90 per cent carbohydrate and 10-15 per cent protein) come from photosynthesis during the maturation process. In dry conditions, there is no photosynthesis and this results in small, shrivelled grains used only for animal feed. The aim is to increase the ability of the wheat plant to store carbohydrates where they can be transported to the grain in dry conditions, for example in the stems.

Researchers are currently figuring out the biology involved in these processes, so that they can look for molecular markers for breeding, Richards said.

In addition to CSIRO's efforts, the CRC for Molecular Plant Breeding scientists are also developing drought tolerant cereal crops, specifically wheat and barley.

Dr Hugh Wallwork, the CRC's genetics and molecular marker technology program leader, said the CRC was focusing on two approaches, using the existing variation in the crops and looking for novel genes in other species to be transferred into the crops.

For a start, the CRC's researchers are looking at the variation already present in wheat and barley. One project in collaboration with the International Maize and Wheat Improvement Centre (CIMMYT) is examining the genetics of drought tolerance in wheat to try to identify molecular markers than can then be used for breeding purposes.

In barley, the researchers are looking for drought tolerant genes in wild barley that can be transferred into the cultivated varieties.

"Our main role is to do the genetics and transfer those resistances to our crops," said Wallwork. "The key is understanding the genetics."

The CRC is also looking at a number of individual traits that would enhance drought tolerance. Wallwork said subsoil constraints such as salinity and root disease all affected a plant's ability to tolerate dry conditions.

"It will never be a drought tolerance gene per se, it will be a combination of things," he explained.