Root System Plasticity to Drought Mitigates Grain-Yield Depression in Wheat

Root characteristics and plasticity to drought may reduce the negative impact of drought on crop yield. Four near-isogenic wheat-rye translocation lines were used to test the hypothesis that root-system plasticity to drought influences grain yield in wheat. Bread wheat 'Pavon 76' and its 1RS translocation lines 'Pavon 1RS.1AL', 'Pavon 1RS.1BL' and Pavon '1RS.1DL' were evaluated for root allocation and plasticity in sand-tube experiments under well watered and droughted conditions over 2 years using factorial treatments in a randomized complete block design with 4 replicates. The 1RS translocation lines had greater root biomass per plant ranging from 7.37 to 8.60 compared to 5.81 for Pavon 76. Only Pavon 76 showed a positive response to drought by producing more shallow roots (developed between 0 - 30 cm) and deep roots (developed below 30 cm) in droughted conditions than in well watered conditions. At drought intensity of 19% (measured as overall reduction in grain yield), yield in Pavon 76 was reduced only by 11% compared to other genotypes with yield reductions ranging from 18 to 24%. However, at drought intensity of 36%, grain yield in Pavon 76 showed maximum reduction indicating greater root production under stress is advantageous only when plant-available water is sufficient to support grain production. Grain yield was positively correlated with shallow and deep root weight and root biomass under terminal drought. Correlation coefficients between root-system components and phenological periods were not significant. The study indicated gene(s) influencing adaptive phenotypic plasticity of roots to drought are located on chromosome 1BS.