Unlocking the genetic potential of the root system, rhizosheath mucilage and microbiome of wheat (Triticum aestivum L.)

An increasing global population, projections of climates that will challenge sufficient crop production, and a detrimental use of fertiliser and pesticides mean that we need to increase the productivity of land currently under cultivation with minimal impact on the environment. Wheat is the second largest contributor to global crop production and is cultivated across a range of latitudes across both hemispheres. The wheat root system is a crucial determinant of plant performance, yet roots are overlooked in breeding due to the challenge of studying organs below ground. Evidence from the literature indicate that water and nutrient uptake are often suboptimal in high yielding and stressed environments. Facilitating the incorporation of root system characteristics into breeding programmes and developing crop management strategies that enhance root function could be key to increasing yield potential and stability, while minimising inputs. To fill the knowledge gap on root-rhizosphere-yield interactions the research presented here falls into three strategic areas: root system architecture (RSA), root secretions and the rhizosphere microbiome. 1) Genetic mapping of RSA in the Avalon x Cadenza Doubled Haploid (AxC) mapping population identified quantitative trait loci (QTL) for seedling seminal root angle, length and growth rate. Replicable QTLs were associated with root angle and mapped to chromosomes 3A and 4D, explaining 7% of phenotypic variation. After extensive root phenotyping, the tails displaying phenotypes at the extremes of the population distribution were taken forward for field trials. Correlations between seedling root phenotypes and the root and canopy phenotypes of mature plants grown in the field were calculated. 2) Root secretions represent a significant loss of fixed carbon from the plant, yet they are thought to confer benefits in relation to plant water status, nutrition, salinity stress, microbial interactions and the development of the rhizosheath. Enzyme-linked immunosorbent assays (ELISAs) were used to quantify the amount of high molecular weight polysaccharides in the rhizosheath of AxC tails, determine the influence of genotype on secretion and investigate potential interactions with RSA. 3) A metagenomics study of the microbial population within the rhizosheath of AxC tails uncovered differences in microbial community composition between lines of the same species. iii Lines grouped according to phenotype (level of secretion, RSA, yield) showed that the microbiome of high-yielding lines differed from that of low-yielding lines. The level of secreted polysaccharides was associated with differences in the microbiome. Overall, this research presents a novel, multi-faceted study of the root system, from seedling to mature plant in the field, as a holistic approach to crop improvement is more robust than the unlikely discovery of a “silver bullet”.