Variation in specific root length among 23 wheat genotypes affects leaf δ 13 C and yield

Abstract

Abstract Identifying root traits that are associated with efficient nutrient and water utilization is crucial for improving plant functioning and productivity. In the case of wheat genotypes, such root traits could be used by plant breeders to improve grain yield and quality. In this study 23 wheat genotypes (Triticum spp.) belonging to different breeding groups were planted in a randomized block design field experiment in NSW, Australia and fertilized with 100 (LN) and 234 kg N ha−1 (HN). Root traits were measured at stem elongation, and aboveground plant material was collected at stem elongation, grain filling and plant maturity. Differences in specific root length (SRL, the ratio of root length to dry mass) among genotypes confirmed their genotypic variability. SRL in the topsoil at stem elongation was a good predictor of leaf δ13C (a proxy of leaf-scale water use efficiency, WUEi) both at grain filling and at plant maturity, and of grain yield in both LN and HN treatments. Notably, genotypes with higher SRL (longer and thinner roots) had a higher leaf δ13C (i.e. higher WUEi) and N concentrations and were associated with lower grain yield. High N rates increased leaf δ13C and N concentrations without overall increasing grain yield. Genotypes with higher SRL were more responsive to higher rates of fertilization producing leaves with higher N and grain with higher protein concentrations. Therefore, SRL is a key root trait affecting grain yield through control on soil water uptake, and affecting grain quality through control on soil N uptake when N availability is high. We suggest that SRL should be considered by plant breeding schemes as a target trait to modify grain yield and quality.