The focus on wheat yield gains has sharpened considerably since estimates back in 2012 found that existing rates of improvement were not going to keep pace with rising demand. The world's response was the US$100 million International Wheat Yield Partnership (IWYP).
With the first round of funded scientists due to report in 2019, the IWYP has announced the first recipient of second-round funding.
The new project's target is diversity in wheat root systems. The goal is to develop germplasm for breeders that can deliver root configurations best suited to different soil types and growing conditions. With better-adapted roots come opportunities to improve crop performance, particularly yield stability during tough seasons.
This root optimisation work is now widely acknowledged as a key component for increasing yield potential and stability, offering new avenues to improve water and nutrient use efficiency.
Taking part is a coalition of laboratories in Australia, the UK, Germany, Italy and Mexico, including the International Maize and Wheat Improvement Center (CIMMYT), which is responsible for breeding the highly adaptable wheat varieties used extensively around the world, including in Australian breeding programs. The project is headed by Dr Eric Ober of the National Institute of Agricultural Botany (NIAB) in Germany.
The yield challenge
The project recognises that wheat is one of the most important staple crops but that its production is being adversely affected by global drought in the world's major growing regions. Cultivars better adapted to increasingly harsh seasons are urgently required, particularly in marginal regions where growing conditions are already challenging.
Since roots represent the primary interface for resource acquisition, different root architecture presents opportunities to optimise this function for various soil profiles, water availability and rates of nutrient availability.
The challenge is to ensure that the optimised root systems are efficient, meaning they drain away as little carbon as possible from grain filling.
To achieve this feat, the project is drawing on a decade of foundational research that developed non-destructive tools to measure root architecture. This includes efforts developed by Dr Michelle Watts (formerly of CSIRO but now based in Germany) that uses MRI (magnetic resonance imaging) to visualise - at high resolution and non-destructively - the roots of plants grown in large cylinders.
The ability to measure root architecture also served as a vital stepping-stone towards mapping genetic control of root structure and function onto the bread wheat genome. This resulted in the development of DNA markers that are important for the rapid selection of root traits during pre-breeding.
Root science comes of age
The recently developed root phenotyping and genomic tools are now being applied to quickly develop a new breeding resource for adapting the root architecture of high-performing wheat varieties to the challenges of local environments.
The output is not so much a new variety but a population of that variety that is genetically identical but expresses a range of different root systems.
The project starts with a collection of wheat lines - including some relatively wild landraces - that possess interesting variation in root architecture. Elite wheat varieties are then selected and a range of different root systems are crossed into the elite germplasm. Back-crossing with the elite variety is then used to restore its high performing genetics.
The output is not so much a new variety but a population of that variety that is genetically identical but expresses a range of different root systems. Those populations are then extensively field-tested in different environments and seasons to determine yield attributes and resilience.
The project's Australian node is responsible for this early development work to create the root-variant wheat populations. It is led by Dr Kai Voss-Fels and Dr Lee Hickey of the Queensland Alliance for Agriculture and Food Innovation (QAAFI) and it is funded with investment from GRDC.
Pre-breeding underway
The root-oriented pre-breeding got underway late in 2018. Four standout wheat varieties were selected to have their roots architecture diversified.
Of the four varieties, two are Australian-adapted elite varieties that together provide adaptation to a broad range of Australian growing conditions: Suntop (PBR) and Mace (PBR). The other two are the highly adaptable CIMMYT varieties Borlaug100 and Kingbird.
An enormous number of crosses are required to introduce a range of different root characteristics into this elite material. Normally, performing the transfer and back-crossing would blow out the development time before field trials could begin to validate the value of the root traits.
However, by taking the lead, the QAAFI team is able to use the speed breedingfacilities developed by Dr Mark Dieters and Dr Lee Hickey. This technique can process six generations of wheat in one year. That acceleration is what makes it possible to have the varieties containing a diversity of root architecture ready to bulk up and distribute for field trials in 2021.
The field trials are due to take place in different environments by project collaborators and industry partners at sites in Australia and at CIMMYT's facilities in Mexico, where specialised facilities allow large-scale, routine testing of plant performance under harsh growing conditions, including heat and drought.
As to the type of root architecture, it's not about targeting deeper roots or shallow-wide roots. Rather, the aim is to assemble a good sample of the diversity available in the broader wheat gene pool, including from wild wheat relatives, to test under realistic growing conditions.
The importance of this work
This root optimisation work is now widely acknowledged as a key component for increasing yield potential and stability, offering new avenues to improve water and nutrient use efficiency.
The new project partly stems from the recent discovery at the QAAFI laboratories that the VRN1 gene - which is known to regulate flowering time in wheat and barley - also plays a role in the plant's architecture below ground. The gene helps direct root growth and influences the overall shape of the root system.
This dual role by one gene limits the ability to change the root system when developing new varieties with optimal flowering time. That's the constraint this project is breaking: the ability to develop elite varieties with a range of distinct root systems.
Genetic maps and DNA markers linked to genetic controls of root architecture further help us to achieve this goal.
The project is also helping to train the next generation of crop researchers, by supporting Charlotte Rambla, a new PhD student who will work closely with overseas collaborators and collect valuable field data to validate the role of the root system on yield.
GRDC Research Code: UOQ1801-002RTX
Contact: QAAFI Centre for Crop Science, The University of Queensland, Dr Lee Hickey, T.+61 (0)7 3365 4805 E. l.hickey@uq.edu.au, @DrHikov or Dr Kai Voss-Fels T. +61 (0)7 334 62288 E. k.vossfels@uq.edu.au
Original article published in GRDC Groundcover on 18 April 2018 Diversification of wheat root genetics gets underway.
