Breakthrough finds wheat's vital sleeper gene

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Image of Dr Daryl Mares

Dr Daryl Mares

PHOTO: Emma Leonard

Two bread wheat genes that provide resistance to pre-harvest sprouting – one of the main impediments to consistent grain quality – have been identified by CSIRO’s Agriculture Flagship in a GRDC project.

Pre-harvest sprouting is induced by rainfall between maturity and harvest when premature germination causes a downgrade of grain quality from premium to feed grades and also reduces yield.

It is also a bane for breeders, who cannot readily observe the tendency towards pre-harvest sprouting in their breeding lines if conditions during field trials are dry. This is a circumstance that has previously led to the production of wheat varieties that are susceptible to pre-harvest sprouting and catch growers out when a season has a wet finish.

However, pre-harvest sprouting and the associated loss of quality – and income – can be suppressed genetically. A source of pre-harvest sprouting resistance was first discovered in 2001 in the genome of an African wheat landrace by Dr Daryl Mares at the University of Adelaide.

The resistance was thought to be due to the existence of genes collectively called ‘dormancy genes’ because of their ability to suppress germination (keep seed asleep, so to speak) under conditions that would otherwise lead to pre-harvest sprouting.

Since that important discovery, many scientists around the world have been working hard to identify dormancy genes and in the process produce the DNA-based tools that breeders need to select for resistance to pre-harvest sprouting. Those efforts needed further refinement until CSIRO developed techniques to fast-track gene discoveries from bread wheat’s vast genome.

CSIRO’s novel strategy – which has been named the ‘QTL-to-gene pipeline’– has resulted in the first-ever isolation of not just one but two dormancy genes with which to suppress pre-harvest sprouting in Australian wheat varieties.

Further, CSIRO team members Dr Frank Gubler and Dr Jose Barrero say the approach is applicable not only to other dormancy genes lurking in as-yet untargeted regions of the wheat genome, but also to many other agronomically important traits, including greater tolerance to environmental stresses.

"It means we can now analyse crop performance in the paddock, observe useful traits and convert that understanding into gene discoveries, no matter the trait of interest," Dr Gubler says. "The genes then provide ‘perfect markers’ that simplify trait selection within breeding programs."

Breeders have been alerted to the existence of the new markers through a GRDC mailing list and Dr Gubler reports that interest has been high both from Australian breeders and from the international scientific community.

Dr Marie Appelbee, soft wheat and trait breeder at LongReach Plant Breeders, says the resistance to pre-harvest sprouting provided by dormancy genes is a trait she is now targeting as a priority.

“These gene discoveries are a terrific breakthrough,” she says. “It has resulted in markers we wanted and needed. They give us enough dormancy to avoid situations such as the development of LongReach Lincoln and Gladius, which were developed during dry years and subsequently proved highly prone to pre-harvest sprouting if there was late-season rain.”

She says the opportunity has now been presented to avoid highly susceptible material.

Critical to the development of the QTL-to-gene pipeline that delivered the dormancy genes were outputs from two previous CSIRO projects.

Dr Barrero says that of particular importance was a dense genetic map that accurately identified regions (quantitative trait loci, or QTLs) within the bread wheat genome that were associated with grain dormancy. The second linchpin was a wheat population created by Dr Colin Cavanagh (previously of CSIRO but now with Bayer CropScience) that is especially suited to achieving gene discoveries.

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Feature:

Science to help wheat sleep through pre-harvest rain

GRDC Project Code CFF00003

Region National