(From left) Federico Ribalta, Janine Croser, Christine Munday, Marie Claire Castello and Karen Nelson, researchers on the GRDC project into accelerating pulse breeding using assisted single seed descent.
PHOTO: Evan Collis
Scientists can now put pulses through multiple generations in just one year in a breakthrough that significantly reduces pulse breeding times, bringing them on par with cereal and oilseed programs
- Newly developed technique makes it possible to put pulses through multiple generations in just one year
- The new technique locks-in valuable new combinations of plant traits so they are stably inherited
- The technology is established for lupins and lentils and now being applied to chickpeas and field peas
A step-change has been achieved in technology that speeds up the breeding of improved pulse varieties, potentially breaking the time lag that has kept these crops languishing behind developments for cereals and oilseeds.
Locking-in improved varietal traits in pulses has been comparatively difficult because at least six generations are needed to produce what scientists call a ‘near-homozygous line’.
For cereals and oilseeds – but not for pulses – a shortcut exists in the form of doubled haploid technology. This achieves the desired end result in a single laboratory-based generation in which a seedling is generated from a single cell in less than a year.
Breeding programs must cycle through the production and evaluation of thousands of genetically novel progeny to identify any new traits or 'genotypes'. A technique is then needed to lock in that unique combination of attributes so that it can be stably inherited over many generations. Only then can the line be subjected to full genetic analysis or released as a variety. The faster that 'lock-in' technology works, the less narrow the bottleneck in the breeding cycle.
In an important pre-breeding breakthrough for pulse crops, a team led by Assistant Research Professor Janine Croser, from the Centre for Plant Genetics and Breeding in Western Australia, has develop technology that reduces the time needed to produce near-homozygous lines in pulses.
The new technology stands to play an important role in accelerating variety development in pulse breeding programs.
Initially the team attempted to modify doubled haploid protocols for pulses working with French and Canadian researchers. However, Assistant Professor Croser says this technology (and other inter-generational technologies such as transgenics and gene knockouts) are capricious in that they work in some lines (or genotypes) but not others. This proved to be the case for pulses, with the formation of double haploids being very hit-and-miss.
So the Centre for Plant Genetics and Breeding team opted to switch strategies and has succeeded in developing a robust alternative approach to doubled haploids that delivers equivalent time savings. It is called assisted single seed descent (SSD).
Initially the technology was applied to lupins and lentils, but in a second phase of the GRDC-funded project this focus has now been expanded to include chickpeas and field peas.
“The technique developed for pulses works on the same principle as SSD in which a population of inbred plants is derived by self-pollinating individuals for several generations,” Assistant Professor Croser says. “We modified the procedure so we can run through it much faster.
“For lupins, lentils, field peas and chickpeas, we can now turn over five to eight generations in a year – that’s approximately the same time required to produce a doubled haploid line (seed-to-seed) in cereals.”
The technique involves two phases. In the first phase, seed from the lines of interest – be it the breeding lines or a mapping population used to identify the gene variants associated with a trait of interest – are grown under controlled conditions that accelerate growth. Protocols to achieve this growth acceleration were determined for each species included in the project.
The second phase draws on embryology studies performed at the Centre for Plant Genetics and Breeding, which determined the earliest time that an immature seed can be harvested.
This second-generation seedling then starts the process over again, under the care of an expert research team comprising Christine Munday, Federico Ribalta, Kylie Edwards, Karen Nelson and Dr Marie Claire Castello.
So far, the assisted SSD technique has worked for all genotypes tested; however, validation experiments across even more genotypes are ongoing.
The technology has been developed in such a way that characteristics of individual plants, including genetic and phenotypic analysis for important disease and stress-tolerance traits, could be possible.
The system can accommodate high-throughput marker-assisted selection, for example, by taking a leaf from the plant as it is growing.
“We are also progressing towards screening for disease and abiotic stresses such as boron and salinity that can be done at the seedling stage under controlled environment conditions. We see that extra testing capacity as an important value-add to this technology.”
For traits that require field trials in specialised environments, assisted SSD technology could be applied from a later generation to accommodate that testing.
As such, the assisted SSD technology can provide important services to pre-breeders undertaking trait-discovery projects, in addition to being valuable to breeding programs.
“The technology has applications all over the variety-development pipeline,” Assistant Professor Croser says. “That is why we are excited. We can see there are a number of end-users who would find it beneficial for their research.”
She is particularly keen to see the technology used to develop a faster, more proactive R&D pipeline for pulses, with the capacity to respond to emerging crises faster than in the past.
She cites the 1998 ascochyta blight outbreak in chickpeas as an example. She says pathologists were seeing signs of an emerging crisis and the genetics were available within international germplasm to respond to the disease. However, the disease-tolerance trait hit a bottleneck since it had to be transferred into locally adapted cultivars.
“It took breeders time to respond to that disease outbreak predominantly because it takes such a long time to breed,” she says. “Growers lost confidence in chickpeas. It has taken a decade or more for the industry to recover.”
Raised on a farm in the Wimmera, Assistant Professor Croser found the ascochyta blight experience especially frustrating, which helped fuel her long-standing interest in technology that reduces breeding times.
“I see this technology as oiling the wheels of breeding to make everything move faster.”
Assistant Professor Janine Croser,
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