Stay-green wheat may weaken drought’s grip

A novel combination of drought-tolerant ‘stay-green’ traits is being brought together in some of the best-performing Australian wheat varieties to produce breeding lines for a significant step-up in crops able to lift yields in dry conditions.

Stay-green was discovered in wheat more than 25 years ago, but the traits are only now becoming accessible to breeders through the development of molecular markers, the details of which will be published this year.

The breakthrough has been achieved by Queensland scientists who are combining stay-green canopy with root architecture traits. These enable wheat plants to ‘stay green’ after flowering: optimising grain-fill even in drought conditions.

The research stems from the Queensland Alliance for Agriculture and Food Innovation. Through this collaboration between the University of Queensland (UQ) and the Queensland Department of Agriculture, Fisheries and Forestry, researchers are now transferring the stay-green trait combination to the high-yielding, disease-resistant wheat cultivars Mace, LongReach Scout and Suntop.

UQ’s Dr Jack Christopher says the new combination of drought-adapted traits has the potential to provide a 12 per cent lift in rain-fed wheat yields in dry conditions.

Leading the GRDC-funded research, Dr Christopher says breeding companies should have wheat lines including the stay-green genes by 2017. This mix of drought-adapted traits has proven elusive due to its complexity, until recent advances in breeding technologies.

Stay-green in plants can be determined by a range of underlying mechanisms, several of which facilitate increased water availability after flowering, such as small canopy size at flowering, increased moisture uptake after flowering, increased nitrogen uptake during grain-fill and increased nitrogen in leaves.

One benefit of such complexity is that it led scientists to look for genetic clues in the root systems of stay-green wheat plants.

They found a narrow root structure with more roots at depth could extract more moisture from deep in the soil during grain-fill, resulting in an extra 500 kilograms per hectare of wheat per 10 millimetres of soil moisture taken up after flowering.

When it was also found that the root traits had improved wheat yields independently of stay-green canopy traits they were also added to the genetic combination being sought for drought tolerance.

Now Dr Christopher says “an explosion of sophisticated new pre-breeding technologies” is helping to speed up the transfer of these drought-adapted genes into commercial wheat lines.

Molecular markers and rapid phenotyping for stay-green wheat represent a major advance in these extremely complex traits – especially when combining influences from plant parts above and below the soil surface and across different growth stages.

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