Yield, grain quality, tolerance to abiotic stress and disease resistance are important, yet challenging targets for breeders aiming to improve wheat productivity. Such attributes, often quantitative traits, interact with both the environment and farm management practices.
To unravel the genetics of these complex traits, we have rapidly developed a multi-parent reference nested association mapping population (MR NAM). This was developed by nesting 11 diverse founders within three common parents adapted to the western, southern and northern cropping regions of Australia - see diagram below.
Founders were selected based on key target traits involved in drought and heat adaptation including stay-green root architecture, heat tolerance, and transpiration efficiency, disease resistance including crown rot and rust, and acid soil tolerance including to manganese and aluminium. Recombinant inbred lines (RILs) were derived using an incomplete factorial design crossing scheme, producing over 1,000 F4-derived lines consisting of 15 families. The MR NAM population was genotyped using the DArT-seq genotype-by-sequencing platform, generating over 25,000 polymorphic markers. Each year, new founders are being added to increase the population size and genetic diversity.
This evolving population represents an unprecedented public genetic resource available to wheat geneticists, physiologists, pathologists, and breeders to unlock the genetic potential of wheat in Australia. In addition to increasing productivity, improved tolerance to abiotic and biotic stresses can lead to expansion of wheat production areas, such as in sub-tropical and tropical environments in Australia and world-wide.
Diagram illustrating development of the multi-reference parent nested association mapping population:
Genome reshuffling occurred between 11 founders and three reference parents throughout crossing and development of recombinant inbred lines (RIL) via four generations of self-fertilizing. The three related nested association mapping (rNAM) populations consist of three conventional NAM populations, related by common founders. The final multi-reference parent (MR) NAM comprised 15 families: four Mace-derived families (Ma-NAM), five Scout-derived families (Sc-NAM), and six Suntop-derived families (Su-NAM). This diagram generated by Cecile Richard