Nested Association Mapping of wheat yield under Australian drought and heat conditions

Abstract

Drought and heat stress are the major abiotic stresses limiting wheat productivity globally. In the 2019-20 season, wheat production in Australia was affected by drought and heat stress resulting in yield losses of up to 18% and monetary loss of about Aus$2 Billion. Breeding wheat with tolerance to drought and heat stress is a sustainable approach to enhancing wheat productivity and ensuring food security in the face of climate change and an increasing world population. Success in breeding is dependent on the availability of genetic diversity, knowledge of the genetic architecture of the traits of interest and efficient means of transferring the desired genetic diversity into the relevant genetic background. Nested association mapping (NAM) populations are valuable genetic resources that enable incorporation of genetic diversity, dissection of complex traits and providing germplasm to breeding programs. A wheat NAM population, with commercial varieties, Gladius and Scout each crossed to a set of exotic lines, was developed as a way of increasing genetic diversity, understanding the underlying genetic architecture of drought and heat stress tolerance and ultimately enhance wheat productivity under Australian hot and dry climate The first focus of this project was to evaluate the genetic properties and utility of the NAM population in identifying genomic regions associated with quantitative traits. Genetic characterisation of the population revealed three distinct groups: the exotic parents, the Gladius families and Scout families. The overall genome wide proportions of exotic alleles across all the Gladius and Scout families was 27.7% and 21.9% respectively. Exotic alleles covered up to 42% of individual chromosomes. Furthermore, previously known and novel genomic regions associated with maturity and plant height were identified. These results validated the usefulness of the NAM population in extending genetic diversity and QTL mapping. The second focus of this project was to phenotypically evaluate the NAM population across various Australian wheat growing environments and seasons in multi-environment trials (METs) and identify stable genomic regions associated with grain yield and yield related traits across diverse environments. A total of 98 genomic marker trait associations were detected for grain yield, thousand grain weight, screenings and hectolitre weight. The exotic parents contributed the most favourable alleles for all the traits. Two recombinant inbred lines which had consistently high yield in multiple environments were also identified. These findings suggest potential genomic regions of interest that could be targeted by breeders to improve wheat yields. The consistently high yielding lines present useful germplasm that could also be of use in breeding programs. The third focus of this project was to assess the genetic differences in the genomic regions associated with grain yield, thousand grain weight, screenings and hectolitre weight of the NAM parents. Genetic differences that result in the coding of different proteins points to useful variation that can be used by breeders. Findings from this study will help to understand the genetic and molecular basis of grain yield and yield related traits.