Relationship between root morphology and grain yield of wheat in north-western NSW, Australia

Abstract Roots are crucial for water up take and nutrient supply both under water limiting and non-limiting conditions, thus influencing crop water-use-efficiency (WUE) and grain yield. The field experiments were conducted in relatively dry conditions in 2009 to assess the impact of genotypic variation for root traits on WUE and yield. Fifteen wheat genotypes were planted in alpha-lattice designs with three replications and tested under high and low moisture regimes. Genetic variability in root length, root diameter and root length density was determined and the impact of these root traits on above ground traits, water use, water use efficiency and productivity assessed. Significant variation in all root traits was observed among wheat genotypes in both high and low moisture environments. A significant reduction in the overall expression of these root traits was observed in response to water stress. Maximum root trait values were observed near the surface (0-15 cm depth) and these decreased with depth with the exception of root diameter in non-water limiting conditions. Mean root length density in both environments was greater than 0.5 cm 3 cm -3 which was considered sufficient to extract all the moisture from the soil. All root traits were highly heritable and the synthetic derived genotypes were generally superior for all root traits and produced higher grain yield and superior WUE. Stronger relationships between root and above ground traits were observed when water was not limiting. Root traits collectively contributed between 31 and 45% of total variance in improved WUE and grain yield, respectively under water stress and genotypes were identified that extracted water more efficiently under drought resulting in improved WUE and grain yield. It is concluded that under water stress, crop water extraction and adaptation depends on root distribution. The genotypes with superior root characteristics can be combined in crosses with sources of resistance to root diseases, such as crown rot, to improve the adaptation of wheat in north-western NSW. Key words: water deficit, drought, genetic variation, root traits, water use efficiency, wheat. Abbreviations: TRL_total root length (cm) in 0-60 cm soil depth; TRD_total root diameter (mm) in 0-60 cm soil depth; RLD_root length density (cm cm -3 ) in 0-60 cm soil depth; WU a _crop water use at anthesis; WU m _crop water use at maturity; WUE DM _Maturity_water use efficiency for dry matter production at maturity; WUE Grain _water use efficiency for grain yield