Phenotyping and Genetic Analysis of Root and Shoot Traits of Recombinant Inbred Lines of Bread Wheat Under Well-Watered Conditions

Phenotyping root traits and understanding their inheritance are critical for crop improvement, as the root system plays an important role in crop performance under well-watered and drought conditions. A set of 118 F-8 recombinant inbred lines (RILs) of bread wheat (Triticum aestivum L.) derived from the cross Iran #49 (a landrace) x Yecora Rojo (a standard variety) plus the two parents was used to phenotype root traits at mid-tillering stage and at physiological maturity in sand-tube experiments under well-watered conditions. Iran #49 and Yecora Rojo were different for grain yield per plant (20.4 vs. 13.8), shallow-root weight per plant (5.3 vs. 1.3 g, roots developed between 0 and 30 cm), deep-root weight per plant (4.5 vs. 0.5 g, roots developed below 30 cm), and root biomass per plant (9.8 vs. 1.8 g). Although there were significant differences among the RILs for number of roots longer than 30 cm, total length of roots longer than 30 cm, longest root, shallow-root weight, deep-root weight, and root biomass, the estimate of narrow-sense heritability was relatively low for shallow-root weight (26%), deep-root weight (14%), and root biomass (22%) at mid-tillering stage. At maturity, the estimate of heritability for these root traits was 81%, 79%, and 83%, respectively. Additive x additive epistasis was detected for deep-root weight at maturity. Genotypic differences in root traits among the RILs were highest at maturity. The root traits measured at mid-tillering and at maturity showed significant, but weak correlation coefficients ranging from 0.20 to 0.40. Grain yield per plant showed significant genotypic correlation with root traits at maturity. Harvest index showed strong negative correlation with root traits ranging from -0.69 to -0.78. Our studies indicated that the appropriate time for phenotyping root traits in wheat is at maturity.