Take home messages:

• Since the introduction of hybrids in the 1950s the rate of genetic progress for grain yield has been slow (<1% per year) and in recent years this rate has plataued.
• Causes of slow progress include low genetic diversity, genotype x environment interactions that complicate selection and a focus on defensive traits.
• A combination of the maturing of new technologies and new investment by GRDC and DPI&F offer promise for increasing yield by breeding. The development of sorghum hybrids with some degree of adaptation to specific environment types is likely to be an important part of any progress.

Background

GRDC and the Queensland government jointly fund the DPI&F breeding program, which is the only publicly funded sorghum-breeding program in Australia. The current role of the program is to address strategic industry issues through the development of germplasm and by facilitating R&D. DPI&F no longer develops or evaluates commercial hybrids rather it generates germplasm lines whose benefits are delivered to grain growers via the private seed companies. The breeding program has a long history of developing lines with midge resistance and more recently stay-green. Lately with new investment from GRDC and DPI&F the focus of the program has changed to increasing grain yield via breeding while maintaining acceptable levels of midge resistance and stay-green. This update reports on aspects of current research in the program and its potential increasing sorghum yields by breeding.

Grain yield

Since the introduction of hybrids in the 1950s the rate of genetic progress for grain yield has been slow (<1% per year) and this slow rate of progress has plateaued. The causes of this slow rate of progress are low levels of genetic diversity in elite sorghum, a strong focus on breeding for defensive traits and genotype by environment interactions that complicate selection. DPI&F is using three strategies to improve sorghum yield.

1) Increasing genetic diversity

The genetic diversity of Australian elite sorghum is relatively low and is potentially reducing progress for grain yield. The DPI&F sorghum-breeding program has a large Bring in genetic diversity while maintaining current levels of midge resistance and stay-green. The program consists of identify useful germplasm from around the world and using it to produce populations with good levels of midge resistance and stay-green. Progress to date has been promising.

2) Trait based breeding

The program is working on specific traits though have the potential to increase yield in Australian environments. Stay-green is a good example of this trait-based approach. Stay-green results in increased grain yield when crops are subject to water stress after flowering. Height in sorghum is strongly correlated with grain yield with taller sorghum varieties yielding more on average than short ones. Tall genotypes have a greater tendency to lodge and sorghum breeders have generally selected for shorter types. The improvement in standability that has occurred as a result of stay-green may allow taller higher yielding sorghums to be developed.

3) Specific adaptation

In Australia, there has been a tendency to develop sorghum hybrids with broad adaptation to a range of climatic conditions. The development of sorghum hybrids with specific adaptation to particular types of environments/management systems offers the potential to enhance yield. These types of systems include low rainfall skip row systems and high rainfall high yield systems. Recent advances in plant physiological modelling and molecular marker technology offer greater scope to develop sorghum hybrids that are suited to particular production/management environments.

Figure 1 : Classification Of 43 DPI&F sorghum trials based on relative hybrid ranking

Group B = CQ & Dry southern environments, Group A= low stress environments

Table 1 : Correlations between yield, stay-green and height (43 breeding trials)

Yield improvement in maize a success story Duvick et al

Sorghum environment types (Chapman et al)

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