Root system plasticity to drought influences grain yield in bread wheat

Crop productivity in semiarid regions is mainly limited by water availability. Root characteristics and plasticity to drought may reduce the negative impact of drought on crop yield. A set of near-isogenic wheat-rye translocation lines was used to test the hypothesis that root system plasticity to drought influences grain yield in wheat. Bread wheat Pavon 76 and 1RS translocation lines, namely 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 across 2 years using factorial treatments in a randomized complete block design with four replicates. The 1RS translocation lines had greater root biomass per plant ranging from 7.37 to 8.6 compared to 5.81 g for Pavon 76. Only Pavon 76 showed a positive response to drought by producing more shallow roots (roots developed between 0 and 30 cm) and deep roots (roots developed below 30 cm) in droughted conditions than in well-watered conditions. Thus at drought intensity of 19% (measured as overall reduction in grain yield), grain yield in Pavon 76 was reduced only by 11% compared to the 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 that greater root production under drought is advantageous only when plant-available water is enough 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 (shallow and deep root weight and root biomass) and phenological periods were not significant. Our study indicated that genes influencing adaptive phenotypic plasticity of the root system to drought in Pavon 76 are located on chromosome 1BS.