Down to Earth with Bob Freebairn: Wheat varieties suitable for deeper sowing

These wheats are no longer an unrealistic hope or fantasy.

CSIRO researcher Dr Greg Rebetzke and his team have been working on developing wheats with longer coleoptiles for several years.

The coleoptile is the protective sheath which encloses the emerging shoot and first leaves.

The longer the coleoptile, the greater the emergence potential when deep sowing.

Longer coleoptile varieties can be capable of germinating when sown at a depth of 100-120 millimetres, compared to 50-70mm for most current varieties.

Since the release of higher-yielding, shorter varieties, from the late 1960s onwards, coleoptile length tended to also be shorter and correlated with plant height.

However, there remains some variability between current varieties even with similar height (for example see NSW DPI 2023 Winter Crop Variety Sowing Guide, page 9).

Sundancer is an example of a newer variety with longer coleoptile than many current varieties, especially in the earlier sowing category.

But further releases will probably see even greater improvements in coleoptile length.

Dr Rebetzke and team identified new genes for longer coleoptiles linked with shorter straw.

These have been incorporated into breeding lines for plant breeders to use in their programs.

To enable more effective breeding these genes are also commonly linked to genetic markers which enables more efficient selection for lines that contain one or more of these genes.

Breeding companies are likely to release varieties with these longer coleoptiles within the next few years.

Long coleoptile wheats in research have established well from sowing as deep as 120mm, far more successfully than typical varieties with shorter coleoptiles.

They also have established well from more normal sowing depths, 40-50mm. But they have the added advantage should deeper sowing be needed.

Research has shown that varieties with longer coleoptile genes can yield much higher than shorter coleoptile ones when deep sowing is required. But they yield much the same if normal sowing depth is possible.

Varieties suited to the earlier sowing window, for many areas mid to late April to mid-May, often have a requirement for deeper sowing.

For example, it is common for summer fallows to have good levels of conserved soil moisture, but where they have dried out on top as a consequence of a late dry summer early autumn.

Being able to sow at 100mm or 120mm depth can reach this moisture for a satisfactory germination whereas sowing at more normal depths means sowing into dry soil.

Research has also shown other factors, regardless of variety or crop, can affect germination.

For example, plump, well-filled seed generally has a longer coleoptile than a smaller or pinched grain.

Soil temperature can also affect coleoptile length. Hotter soils, especially, shorten coleoptile length. It's a real issue if warm conditions occur when sowing dual purpose cereals late summer early autumn.

Dr Rebetzke and team have received extended funding to progress national research aiming to integrate long coleoptile wheats into the Australian farming systems.

Research partners include University of Melbourne, NSW DPI, QLD Department of Agriculture and Forestry, WA Department of Primary Industries and Regional Development, the University of South Australia and EPAG Research.

Research will include national trials to further explore genetic, environmental and management factors relating to long coleoptile wheat.

The project will also include developing a common industry standard for measuring and defining categories for wheat coleoptile length, for example, normal (80mm), long (80-100mm) and super long (100mm-plus).

Next week: Selecting winter legumes for next autumns sowing. Some newer varieties worth considering.