Developing acid-soil-tolerant faba bean varieties to expand faba bean adaption.

Faba bean production in Australia is constrained by soil acidity, particularly in Western Australia, South Australia, southern New South Wales and parts of Victoria, where acidic soils reduce root growth, nodulation, nitrogen fixation, crop vigour and grain yield. Soil acidity also limits the expansion of faba bean into otherwise suitable production environments. While liming remains an important soil management practice, sub-surface acidity is often difficult, slow and costly to remediate, creating a need for complementary genetic solutions that improve crop performance and profitability on affected soils. Recent GRDC investments have successfully delivered acid-tolerant rhizobia for faba bean, improving nodulation and nitrogen fixation under low pH conditions. However, the effectiveness of these inoculants depends on successful plant-rhizobia interactions, and current elite faba bean germplasm remains poorly adapted to acid soils (pH (CaCl2) <5.0). Developing acid-soil-tolerant varieties is therefore essential to fully realise the benefits of improved rhizobia strains and maximise productivity in acidic soil environments. This four-year investment will accelerate the development of acid-soil-tolerant faba bean varieties by delivering the germplasm, genetic knowledge and breeding tools required to support long-term genetic improvement. The investment will identify and validate novel sources of acid soil tolerance from Australian and international germplasm, improve understanding of the physiological, biochemical and genetic mechanisms underpinning tolerance, and translate these discoveries into practical breeding outcomes for Australian faba bean breeding programs. Controlled-environment screening, field-based validation and modern genomic approaches will identify and characterise traits associated with improved performance on acidic soils, including traits linked to root growth, nodulation, nitrogen fixation, crop establishment and yield. Activities should address both surface and sub-surface soil acidity and generate robust, field-relevant data to support breeding and selection decisions across target production environments. A key component of the investment will be the development of validated high-throughput phenotyping methods, screening protocols and molecular markers that enable efficient selection for acid soil tolerance. These tools will support more rapid and cost-effective identification and deployment of favourable alleles within breeding pipelines, accelerating genetic gain for adaptation to acidic soils. Breeder-ready germplasm will incorporate novel acid-soil-tolerance alleles and demonstrating improved performance under acidic soil conditions, with a target yield advantage of at least 10% over benchmark varieties grown on acid soils of pH (CaCl2) below 5.0. Germplasm should be validated across representative production environments and supported by associated genetic, phenotypic and marker datasets to facilitate immediate use in breeding programs. Strong collaboration with Australian commercial and public faba bean breeding programs will be a core requirement of the investment. Breeding programs should be engaged throughout the project to guide trait prioritisation, validation environments, phenotyping approaches and deployment pathways, ensuring outputs align with breeding priorities and can be rapidly incorporated into breeding pipelines and early-generation selection programs. The intended outcome is to provide Australian breeders with the genetic resources, screening tools and knowledge required to develop future faba bean varieties with improved adaptation to acid soils, enhanced yield stability and increased productivity. These advances will complement existing soil amelioration practices and acid-tolerant rhizobia, support expansion into suitable regions, improve reliability on acid soils and strengthen the competitiveness and sustainability of the Australian faba bean industry.