An innovative tag team of researchers, breeders and statisticians has successfully developed chickpea germplasm that is tolerant to imidazolinone herbicides.

The new material will provide growers with a set of tools to manage the many weed challenges in chickpea crops, including a lack of post-emergent herbicide options and crop damage from soil carryover of previous residual herbicide applications. The development of this material is the product of investment by GRDC and its partners.

The first-generation chickpea material that contains the herbicide tolerance mutation was bred into the PBA Seamer (PBR) variety. Chickpea Breeding Australia breeder Dr Kristy Hobson says this first cultivar will be used to support regulatory approval for the foliar application of an imidazolinone herbicide for post-emergent use in chickpea crops.

The Australian Pesticides and Veterinary Medicines Authority registration application requires at least two years of field study data, including data relating to crop safety, efficacy and grain residues. GRDC is facilitating the generation and collation of the required data with a commercial partner in support of the registration process.

Dr Hobson expects the regulatory process to be completed in late 2023, with the first herbicide-tolerant varieties potentially available as soon as 2024.

She adds the mutation that provides the imidazolinone tolerance is the component that is being registered, not the first-generation variety, which has an important implication. “That means the registration will be valid for all subsequent varieties we develop without additional regulatory approvals, other than the need to demonstrate the presence of the registered mutation,” she says.

With that in mind, growers will benefit from a slew of innovative chickpea cultivars that are under development and that are suited to a range of growing environments. That development includes a both the northern growing region, and southern and western environments.

Accelerated breeding

Throughout the development process, researchers deployed novel techniques that accelerated the development of the herbicide-tolerant chickpea germplasm.

The acceleration started by licensing the use of an imidazolinone tolerance mutation suited to legumes that was previously developed at the South Australian Research and Development Institute (SARDI). That mutation was developed through GRDC and SARDI investment.

Moving the mutation into breeding material was also fast-tracked using the pioneering accelerated-Single-Seed-Descent (aSSD) technology developed by Dr Janine Croser and her team at the University of Western Australia, also as a result of GRDC investment.

At its most effective, this technology can process up to seven generations of legumes in one year, vastly reducing the duration of a breeding cycle. This technology works by manipulating the duration of exposure to light and the light’s wavelength to induce plants to flower and mature sooner.

The field-testing phase also underwent acceleration thanks to the work of maverick statistician Professor Brian Cullis at the University of Wollongong, where he is the director of the Centre for Biometrics and Data Science for Sustainable Primary Industries.

Professor Brian Cullis helped to fast-track the development of imidazolinone-tolerant chickpea varieties using sophisticated statistical methods contained within Incomplete Multi-Environment Trials methods. Photo: Brian Cullis

Professor Cullis works closely with Dr Hobson to ensure that the design of field trials is optimised to produce the most-relevant data possible about the performance of breeding lines across different growing environments. This includes running the analysis on the trial data to help the breeders select the best-performing lines.

The method is called Incomplete Multi-Environment Trials and it has shaved about two years from the chickpea breeding cycle.

This acceleration works by more rapidly understanding the manner of gene-by-environment (GxE) effects at work within a breeding population, thereby allowing for a more-rapid selection of the best-performing lines.

This is achieved by avoiding the need to test all lines produced during each generation of breeding work at multiple sites. Instead, genetic relationships among the lines are exploited to allow for smaller trials at more sites using just samples of the breeding material. Professor Cullis is then able to produce statistically significant insights about how genetic variation in the breeding material responds to different environmental conditions.

“The method fast-tracks a breeder’s ability to identify the best-suited lines for variable environmental conditions,” Professor Cullis says. “This is normally a challenging problem for breeders, but one that we need to get right if we want to release the best-adapted material possible to growers.”

This powerful capability proved especially important with the imidazolinone tolerance project, as it was able to accommodate the lower-than-normal amounts of seed delivered to the breeders by the accelerated aSSD pipeline.

“Incomplete Multi-Environment Trials were ideal for this project,” Dr Hobson says. “We were able to strategically reduce the number of plots we needed, spread them over more environments and yet end up with really important insights about which lines to select and which to recycle as parents for further breeding. We have improved confidence in our selections.”

For Professor Cullis, the project’s success boils down to the collaborative nature of the project that drew on teams with different skill sets and cutting-edge capability.

“The really exciting part for me is that the methods we are using allow us to continuously learn through experimentation,” he says. “That means that as we carry on with this collaboration, we can continue to incrementally improve our capabilities and meet ever-dynamic production challenges.”

More information: Kristy Hobson, kristy.hobson@dpi.nsw.gov.au; Brian Cullis, brian_cullis@uow.edu.au