Cautious optimism for frost-tolerance advance
There is something so perplexing about a frost event and a plant’s response that causes particular trouble for stress-tolerance researchers. Many false starts and disappointments have left pre-breeders wary of announcing progress on frost-tolerance traits for use in plant breeding programs.
However, researchers in Adelaide working with a new screening method and novel sources of genetic diversity appear to be beating the odds, at least for field peas.
Led by Dr Phil Davies, a team from the South Australian Research and Development Institute (SARDI) is half-way through a GRDC project that has the normally sceptical scientists expressing unusual levels of optimism that gains in frost tolerance are possible.
Dr Davies says that in the past two years the team has trialled a new field-based method that has consistently detected variation in frost-tolerance levels among genetically diverse pea lines.
“We are confident enough with the method to state that it can discriminate between genotypes for their frost tolerance,” Dr Davies says.
“We have started to use that method to screen international germplasm; namely a selection of Chinese pea lines collected from chilly, high-altitude sites. We believe there is material in that germplasm with higher levels of frost tolerance compared with what is found in Australian pea varieties.”
Frost was identified by Pulse Breeding Australia (PBA) as a key production issue for field peas more than eight years ago.
“There were earlier efforts to develop frost-tolerant field peas at SARDI using a growth-chamber, but they were unsuccessful for technical reasons relating to the difficulty of mimicking frost events,” Dr Davies says.
With the new project at SARDI, Dr Davies has opted for a back-to-basics approach to screen for frost tolerance.
Just 20 minutes from their base at the University of Adelaide’s Waite Campus on Adelaide’s outskirts, the pulse researchers set up a frost-prone field site at Hahndorf in the Adelaide Hills and fitted the site with its own internet-connected meteorology station.
The station alerts the scientists to a frost event – triggering an exodus from the laboratory to the field site. At Hahndorf, information about the frost event and the plant’s stage of development is tagged on to individual flowers and pods.
At maturity, the researchers return to harvest each plant individually and add information to the tags about the survival of the flower, pods and the seed in the pod. The information captured on the tags is then used to arrive at a figure for the frost tolerance of individual pea lines (stated as the plant’s percentage yield loss).
During 2012 and 2013, the method was used to rank the frost tolerance of Australian field pea varieties. Included was SturtA, the variety that pea breeders intuitively feel is the most frost tolerant.
“The frost-tolerance rankings convinced us that, at the very least, the method gives consistent, verifiable results,” Dr Davies says.
A rare and unusual collection of Chinese field pea germplasm is also being tested. It was especially pre-selected for the frost project by Dr Bob Redden, the curator of the Australian Temperate Fields Crops Collection (ATFCC) in Horsham, Victoria, now integrated into the Australian Grains Genebank, also in Horsham.
“If it wasn’t for Dr Redden’s diligent work, we would not have known where to look for frost-tolerance traits,” Dr Davies says. “His work collecting and researching genetic resources has been invaluable.”
Dr Redden says the peas screened by SARDI were collected in 2004–07 during a mission funded by the Australian Centre for International Agricultural Research (ACIAR). Material collected produced spectacular gains in the genetic diversity of field peas.
Led by Dr Redden, the ACIAR project first collected pea and faba bean landraces (village varieties) from across China and then the two collaborating nations exchanged germplasm.
China received advanced breeding lines from the Horsham breeding program and Australia is the only nation to have access to the Chinese landraces, with a replica of the collection stored at the Svalbard Global Seed Vault in Norway.
Research on these new genetic resources subsequently established that Chinese peas are genetically distinct from peas derived from the Fertile Crescent – the source of Australia’s frost-sensitive varieties. As such, the Chinese material is proving a valuable source of unprecedented diversity and novel traits.
“There is a big benefit from bringing new germplasm to Australia and getting it evaluated,” Dr Redden says. “For the Chinese pulses, this evaluation is ongoing for frost, heat, drought and salinity tolerance.”
Dr Redden also aids trait discovery on behalf of pre-breeders by applying his own variation of the focused identification of germplasm strategy (FIGS) technique. This involves collating information about the collection site’s environment, climate and geography and using it to deduce the sort of specialist traits required by plants to survive at each site.
This allows Dr Redden to pre-select a subset of accessions of interest to individual teams of Australian pre-breeders.For the frost-tolerance project, Dr Redden focused on germplasm collected in mountainous area at altitudes higher than 2000 metres. Among this pre-selected material were several lines with frost tolerance ranked well above Australian varieties at the Adelaide field site. That means following a frost, the flowers are less likely to abort and the seed in the pod is less likely to die.
The pre-selection work by the ATFCC ultimately meant that the SARDI team needed to screen only 150 Chinese lines to identify improved sources of frost tolerance.
The pea lines were ranked according to a yield loss index.
“I always feel nervous reporting on these findings but the results are encouraging and I am happy with the method,” Dr Davies says. “I think we have enough evidence that there are some lines that tolerate frost better than current Australian germplasm.”
Yield loss in the best-performing Chinese line was limited to 30 per cent compared with 90 per cent for the worst-performing Australian variety. However, one Australian variety (Yarram) managed to limit its losses to frost to just 40 per cent and SturtA to about 50 per cent, causing Dr Davies to wonder whether a frost-tolerance trait already exists in the Australian gene pool.
“I don’t yet know whether the Australian and Chinese lines are tolerant through different or similar mechanisms,” Dr Davies says. “What we do know is that the differences we are seeing are not about differences in flowering time and stress avoidance.”
The best Chinese and Australian lines have already been crossed, starting the long process of transferring the Chinese trait into Australian-adapted cultivars. The progeny from those crosses will be field tested in 2014.
“That will tell us whether we can use the lines and this method as a breeding tool in which we use phenotypic selection at Hahndorf to improve frost tolerance,” Dr Davies says.
A similar approach is now also being applied to other pulses, with lupins next in line.
More information:Dr Phil Davies,
Dr Bob Redden,
GRDC Project Code DAS00121, DAV00131
Region Overseas, South, National, North, West