The cooperative relation between non-hydraulic root signals and osmotic adjustment under water stress improves grain formation for spring wheat varieties.

Non-hydraulic root signals (nHRS) and osmotic adjustment (OA) are two important adaptive responses of plants to water stress. There is little understanding of their relationships during water stress. The threshold range of soil water potential to occurrence of nHRS, the capacity for OA, grain yield and water use efficiency (WUE) were examined in three spring wheat (Triticum aestivum L.) varieties (two bred after 1975 and one bred before 1900) under water stress conditions. The threshold range of nHRS was significantly correlated with the maintenance rate of grain yield (MRGY) (r = 0.99, P < 0.05) under moderate drought (-0.49 to -0.55 MPa) but not under severe drought (-0.70 to -0.76 MPa). There were similar correlations between OA and the MRGY. However, regulation of nHRS precedes OA during gradual water stress. The threshold range of nHRS and OA was positively correlated (r = 0.93, P < 0.05), suggesting a mechanism for adapting to drought. WUE was higher for modern than for old varieties and was correlated with the root efficiency (full biomass weight including root per root weight, r = 0.78, P < 0.05) and the root water uptake efficiency (water consumption per root weight, r = 0.72, P < 0.05). However, there was a significant negative correlation between WUE and root weight (r = -0.84, P < 0.01). The cooperative relationship between the threshold range of nHRS and OA under water stress was beneficial for improving grain formation for spring wheat varieties.