An innovative platform that accelerates genetic gain is seen as a major plant-breeding breakthrough that will particularly benefit pulses.

The 'accelerated-Single-Seed-Descent platform', developed by a team from the University of Western Australia (UWA), has already been deployed into Australian cool-season pulse pre-breeding and breeding programs. The platform helps deliver new pulse varieties two to three years faster than conventional breeding techniques by speeding up the rate of genetic gain, as it enables turnover of up to six generations a year in chickpea, lentil, field pea and faba bean.

The UWA team has so far processed 35,000 individual pulse plants to deliver fixed lines to pre-breeding and breeding programs using accelerated-SSD.

This GRDC-invested research provides an excellent example of combining fundamental scientific knowledge in plant light response and seed development with emerging industrial lighting technology to improve breeding efficiency.

Fixing lines after crossing usually takes five to six generations of self-fertilising to achieve. To accelerate fixation of lines, the technique of single-seed descent was adopted in the 1940s. This forms the basis of the accelerated-SSD platform. It relies on quick plant development with low biomass, as only one seed is needed to produce the next generation.

Conventional single-seed descent results in two generations per year in the field across two sites in different climatic regions and three to four generations in glasshouses with artificially extended daylength.

In contrast, by further manipulating growing conditions, the accelerated-SSD platform enables turnover of seven to eight generations per year in chickpea and lentil and five to six generations per year in faba bean and field pea. Plants are grown at high density under tightly controlled environmental conditions. The platform uses extended daylength, late spring temperatures and artificial lighting with spectrum designed to signal to plants they are about to experience shading.

Plants that are not experiencing shade perceive red, green, blue and far-red light spectra in approximately equal quantities. As soon as they begin to be shaded, the ratio of light spectra changes, with everything except the far-red part of the spectrum being reduced through reflection from surrounding leaves.

Light-emitting diode (LED) lighting now enables affordable manipulation of light spectra. The team identified growth under LED lighting with a higher output in the far-red spectrum sends a signal to plants to move through their life cycle as fast as possible to avoid being fully shaded.

By effectively 'triggering' plants into sensing they are about to be shaded, flowering is achieved in as little as 23 days from sowing. These conditions are even effective in inducing fast flowering in lines considered 'late flowering'.

Our new LED technology has been a key mechanism in getting pulse plants to flower quickly and to develop their seed very quickly as well.

To further speed generations, the team developed a seed-treatment process to germinate immature seed, achieving harvest about 18 to 20 days after flowering.

For efficient indoor throughput, plant size is reduced to enable high-density, multi-tier plant growth in the controlled-environment rooms. Plant size is manipulated through growth in small pots and, for faba bean and field pea, through anti-gibberellin application to reduce internode spacing.

The PBA chickpea breeding team, led by Dr Kristy Hobson (NSW Department of Primary Industries), has reduced breeding time further by combining accelerated-SSD with selection for herbicide tolerance traits.

Lines provided by Dr Hobson are grown using the UWA platform and sampled for marker-assisted selection with Dr Tim Sutton's group (SARDI), enabling lines without the trait to be quickly culled, ensuring efficient resource allocation. Dr Hobson predicts combining the two techniques will reduce cultivar development time by three to four years.

The UWA team is further utilising LED know-how to harness genes from wild pulse relatives from the Australian Grains Genebank. For example, by compressing and synchronising flowering of wild relatives and domestic parents of both lentil and chickpea, they are able to be crossed. The accelerated-SSD platform is then deployed to cycle hybrid progeny to fixed lines for field testing up to three years faster than with conventional approaches.

Combining accelerated-SSD with emerging techniques such as genome selection is expected to further reduce time to market of new pulse varieties.

More information: Dr Janine Croser, 0422 702 382, janine.croser@uwa.edu.au