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By Greg Rebetzke Gonzallo Estavillo Kate Langford 11 March 2022 4 min read

This new research is helping to safeguard against a drier climate and potentially generate an extra $2 billion a year nationally for Australian farmers.

Wheat seeds like those of other plants rely on water being available in soil when they are sown so they can germinate and establish before the colder months. A predicted lower autumn rainfall could significantly decrease these sowing opportunities and reduce crop yields worldwide in the future.

Predicted lower autumn rainfall will have a significant impact on wheat production in the future.

But what if seeds could be sown into soil moisture stored deeper in the soil? Could they be grown in times of drought and help farmers adapt to a changing climate? These questions were at the heart of research by CSIRO scientists for a couple of decades.

The work started with an interest among researchers in improving the vigour of wheat seedlings to make leaves larger so they would shade the soil and reduce water loss through soil evaporation. At the same time, growers in central and southern NSW were telling researchers how difficult it was to establish wheat with deeper sowing when ‘chasing deep soil water’.

Enter the coleoptile

The depth that a crop is sown depends on the shoot that grows from the seed to the soil surface, known as the coleoptile. The coleoptile is like a smooth drinking straw that can push through a dry and hard soil allowing the growing wheat leaves to emerge above the ground. Unfortunately, current wheat varieties suitable for Australia develop short coleoptiles.

The wheats with short coleoptile were a trade-off resulting from shorter or “dwarf” wheats developed during the green revolution with the aim of dramatically increasing yields.

As one grower said, “these new dwarf wheats couldn’t push through the skin of a rice pudding.” Another commented, “before dwarf wheats it was rain at harvest that kept me awake at night but now its planting and the need to re-sow”.

Over the past 25 years, CSIRO scientists have developed a better understanding of the physiology and genes that control coleoptile growth from the seed during germination. They have been able to identify new combinations of genes that result in longer wheat coleoptiles without sacrificing yields.

Chief Research Scientist at CSIRO, Dr Greg Rebetzke said this unique plant characteristic could now be a game-changer in environments where water is limited, particularly with dry surface soils at seeding time.

“Instead of waiting for autumn rain, future wheat varieties with long coleoptiles could be planted to depths of 12cm or more and germinate using deeper water stored from summer rains,” Dr Rebetzke said.

The long coleoptile wheat on the left was deep-sown to 12cm. On the right is a dry-sown crop at 4cm. Both were sown at the same time. Photo: Callum Wesley, Southern Cross.

A $2b opportunity

By combining data collected in the field with crop growth models, the CSIRO team has predicted grain yield and put a dollar value on the potential benefits of the long coleoptiles. In a paper published in Nature Climate Change, they estimate that wheat varieties with longer coleoptiles would increase farmers’ profits by a staggering average of $2.3-2.4b/year total annually across Australia.

“Crop modelling enabled the integration of field data and understanding of physiology and genetics to predict the yield benefit of the novel wheat varieties with long coleoptile across contrasting environments”, says lead author and CSIRO crop modeller, Zhigan Zhao.

This has been made possible by the joint effort of geneticist Greg Rebetzke, crop modellers Zhigan Zhao and Enli Wang, and farming systems scientist John Kirkegaard, building on the long-term research on farming systems modelling, genetics and breeding for systems.

The benefit of the long coleoptile is that it ensures the wheat seedling germinates and emerges early and allows growth while current wheat varieties must wait for rain to germinate.

In some parts of the wheatbelt, it is predicted that some seasons will experience up to a six-week delay in the rainfall needed to germinate wheat crops sown into surface soil. Opportunities to manage this variability reduces grower risk.

“Growers can make use of deep moisture if it is there from previous fallow or summer rains. Six weeks extra growth, particularly for very early sown wheat crops, represents a significant gain in biomass and grain yield,” Dr Rebetzke said.

“Along with more efficiant water-use for shoot growth due to the cooler conditions at and after crop emergence, roots are growing at approximately 1 centimetre per day to reach deeper into the soil.”

Callum Wesley, who farms at Southern Cross on the eastern edge of the WA wheatbelt, is already trialling the wheats and has had success in dry seasons.

“In 2020, deep-sown wheat achieved 1.24 t/ha when we only had 86 millimetres of in-season rain following 76 millimetres of summer storms. The deep-sown crop was able to make better use of this summer moisture to increase water productivity to 24 kg/ha/mm compared with only 15 kg/ha/mm in the shallow sown crop,” Mr Wesley said.

“Having this technology will reduce my risk and significantly increase the likelihood of a profitable wheat crop now and with the changes I am seeing in the weather.”

While the long coleoptile wheat varieties are only available to a small part of Australia now, the research team is hopeful they will be made available to more farmers in coming years. Australian breeding companies are now using the new genes together with CSIRO-developed genetic markers to breed new varieties with longer coleoptiles.

CSIRO is also looking at how this research, which combines intricate knowledge of plant genetics with an understanding of particular farming systems, can be translated to other crops to improve the resilience and reliability of Australian farming in future climates.

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