Genome-wide association study reveals genomic regions controlling root and shoot traits at late growth stages in wheat

How much wheat do we need? One prediction is we need production to double between 2005 and 2050. This challenge is more difficult due to abiotic stress with climate change. Long Li and colleagues have been examining root system morphology. Root system morphology is important for sustainable agriculture, but the genetic basis of root traits and their relationship to shoot traits remain to be understood. The aim of this study was to dissect the genetic basis of root traits at late growth stages and its implications on shoot traits in wheat.

Root trait phenotyping. (A) PVC pipes were buried in a soil pit. (B) Soil-filled bags were inserted into each tube. (C) Plants at the jointing stage. (D) Roots were preliminarily washed with a sieve. (E) Roots were further washed in plastic boxes. (F) Minirhizotron pipes were buried in soil with a 45° angle of inclination to measure root traits in each trial plot. (G) Minirhizotron images were collected by a CI-600 Roots Monitoring System. Image: Long Li *et al*. 2019.

Deep-rooted accessions had lower canopy temperature (CT) and higher grain yield per plant (YPP) than those with shallow roots. But no significant relationship was identified between root dry weight and shoot traits. Ninety-three significantly associated loci (SALs) were detected by the mixed linear model, among which three were hub SALs (Co-6A, Co-6B and Co-6D) associated with root depth at both booting and mid-grain fill stages, as well as CT and YPP.

Minirhizotron system scanning results suggested that the causal genes in the three SALs may regulate root elongation in the field. The heritable independence between root depth and PH was demonstrated by linkage disequilibrium analysis. The YPP was significantly higher in genotypes which combined favourable marker alleles (FMAs) for root depth and PH, suggesting that a deep root and shorter plant height are suitable traits for pyramiding target alleles by molecular marker-assisted breeding.

These results uncovered promising genomic regions for functional gene discovery of root traits in the late growth period, enhanced understanding of correlation between root and shoot traits, and will facilitate intensive study on root morphology and breeding through molecular design.