Time for wheat to stand tall

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New research is allowing wheat to join maize and rice as a crop able to gain a yield boost if the plant’s canopy architecture is made more erect.

Photo of CSIRO's Dr Richard Richards

CSIRO's Dr Richard Richards, a pioneer of water-use efficiency traits, has now uncovered a new pathway for lifting wheat yields.

PHOTO: Australian Academy of Science

Key points

  • Yield gains of up to 20 per cent observed in field trials of wheat lines that grow erect canopies.
  • Work continues to delineate the best canopy arrangement for different growing regions, along with optimum row width and plant density.

Trials have shown that wheat yield gains are possible if the canopy architecture of wheat crops is changed. The gains are achieved with leaves that are genetically predisposed to grow in a more erect configuration, a change that also affects on agronomic practices – primarily row width.

Besides making yield gains of up to 20 per cent possible, the trait has attracted international interest for another important reason.

Yield gains in recent decades have been driven by the harvest index (HI) – more grain relative to total straw. However, breeders worldwide believe HI has almost reached its theoretical maximum and so is less likely to contribute to further productivity. In contrast, the erect canopy trait works by boosting photosynthesis and biomass, and creates a new avenue to pursue increased yield potential.

While a similar trait has already benefited maize and rice, this is the first time that canopy architecture has been successfully targeted in wheat.

The advance was made by CSIRO scientists led by Dr Richard Richards, who has been trialling the erect and floppy canopy traits within the GRDC’s high-rainfall zone (HRZ) yield project, led by Dr Penny Riffkin of Agriculture Victoria in Hamilton.

In addition, the trait has attracted the attention of the International Wheat Yield Partnership (IWYP) – a $100 million global program to improve wheat yields through more efficient photosynthesis.

Photo of the IWYP Hub canopy architecture in Mexico

The IWYP Hub canopy architecture experiments in Mexico imaged by a drone managed by Dr Francisco Pinto.

PHOTO: Francisco Pinto

The GRDC has invested substantially in IWYP and the new CSIRO trait is proving pivotal to several IWYP projects that seek yield gains through increased biomass (not HI).

That interest has resulted in CSIRO lines being grown at the IWYP Hub at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico. The IWYP Hub was established to facilitate streamlined delivery of higher-yielding germplasm to growers worldwide, including via CIMMYT’s global wheat breeders.

Floppy versus erect

Wheat varieties predominantly express a floppy canopy architecture. However, theoretically, it has long been considered that crops with erect canopies would have a yield advantage.

Dr Richards says that upright architecture would be expected to better harness sunlight, resulting in higher radiation capture, radiation-use efficiency, biomass and ultimately yield. The highest-yielding maize hybrids, for example, closely follow this theoretical expectation of optimal canopy architecture.

“The odd thing is that the principle is well established,” he says. “Breeders have exploited it in crops such as maize and rice, which are now mostly bred for erect leaf growth. But nobody has followed this up in wheat. This was a neglected area of research and we set out to rectify that.”

To test whether the principle would hold true in wheat, Dr Richards first had to develop wheat lines with altered canopy architecture.

The task was greatly facilitated by the prior GRDC investment in the development at CSIRO of the four-way ‘multi-parent advanced generation inter-cross’ (MAGIC) population (see ‘MAGIC needed to decode wheat genetic secrets’, page 14, GroundCover™ issue 94, September–October 2011). This tool is designed to sample the genetic diversity of Australian wheat varieties within one population, which can then be used to screen for all kinds of traits, including an erect canopy.

Photo of erect wheat canopies

Erect wheat canopies are proving more efficient at harnessing sunlight and converting it into yield.

Photo of floppy wheat canopy

A floppy wheat canopy is the common sight worldwide, but theoretical considerations – and now field trials – have shown that it can be outperformed by erect leaf growth.

PHOTOS: Richard Richards

Field trials

Field trials of CSIRO wheat lines were recently run in the HRZs in Western Australia, Victoria, southern NSW and Tasmania. The lines have also been tested in northern NSW at the University of Sydney Plant Breeding Institute in Narrabri.

Almost no negative associations were found with the erect canopy, making them safe to grow, even when no yield benefit is expected (for example, during a dry year).

However, the trait was found to deliver numerous advantages:

  • yield benefits of up to 20 per cent (10 per cent average), although variation was seen across different sites (including no yield benefit)
  • greater tolerance to high temperatures compared with a floppy canopy
  • greater penetration of sunlight into the canopy, resulting in higher photosynthesis rates, strengthened straw and less lodging and
  • greater green leaf area duration (stay green), fertile tillers and stem carbohydrates.

However, Dr Richards says that higher-yielding growing regions may benefit the most from the erect canopy trait. The reason, he says, is that under very dry conditions wheat tends to produce a more erect canopy anyway, as there is insufficient water for lush, floppy leaves.

“There seems to be a real opportunity here to increase wheat crop productivity in areas such as the HRZs where the yield potential is high,” Dr Richards says. “In dry areas, it is water use efficiency that continues to be more important.”
Agronomic implication

Trials also found that agronomic practices can be used to optimise yield from the erect canopy trait.

This was made clear by the considerable differences in agronomy at different trial sites. The most extreme were in Mexico, with 80 centimetres separating raised beds. Dr Richards now believes that it is this management practice at the CIMMYT trial sites that has promoted the floppy canopy trait in CIMMYT wheat varieties and in all countries that rely on this germplasm, including Australia.

As most countries do not grow wheat on raised beds, Dr Richards has now ensured that trials in Mexico also include more common crop management practices, including flat beds and narrower rows.

Trials in Australia in 2018 will also continue to better delineate this gene-by-management effect for Australian growers, with the GRDC extending its investment in the development of this biomass-enhancing trait.

“We want to reach the point where, based on row spacing, we can advise growers on the optimal canopy type and at what density to grow wheat to maximise yield,” Dr Richards says.

“We do expect to see differences within different growing regions.”

The work continues

Canopy architecture was just one of two yield traits targeted by the GRDC project. The second – called the Ear Construction Phase Duration (CPD) trait – is also delivering yield gains of about five to six per cent across southern Australia.

CPD works by sacrificing vegetative growth to expand the reproductive stage. This trait was also identified in the four-way MAGIC population.

During 2018, Dr Richards will combine the extended CPD and the erect trait into germplasm specifically suited to the HRZ.

One of the parent lines he has selected is the long-season wheat variety Longsword. This a fast-maturing winter wheat derived from Mace that offers a wide sowing window. It is widely adapted to suit WA, South Australia, Victoria and NSW.

He will use accelerated breeding methods (double haploids) to transfer the traits and expects the new winter-type lines to be in the field in 2019.

More information:

Dr Penny Riffkin
penny.riffkin@ecodev.vic.gov.au