Safeners improve early-stage chilling-stress tolerance in sorghum

Sorghum [Sorghum bicolor (L.) Moench] is highly sensitive to chilling temperatures (<15°C soil temperatures) during germination and early seedling establishment. Hence, the main objectives of this research were to (a) validate the potential level of chilling tolerance in selected sorghum genotypes, (b) determine effective concentrations of selected safeners for improving chilling tolerance and (c) determine if safener combinations further enhance chilling tolerance compared to individual safener treatments. Four experiments were conducted with five sorghum genotypes, four safeners (oxabetrinil, fluxofenim, naphthalic anhydride and benoxacor), nine safener concentrations (0–25 μM) and two temperatures. The chilling-tolerant genotypes recorded higher germination percentage (98% vs. 63%) and root (3.0 vs. 0.8 cm) and shoot lengths (0.7 vs. 0.1 cm) compared to sensitive genotypes under continuous 15℃. Each of the four safeners applied at the highest concentrations tested (20 and 25 μM) significantly enhanced seed germination and seedling growth at 15℃. The combination of four safeners was more effective in reducing chilling stress-induced injury compared to individual, two- or three-way combinations. Enhanced chilling tolerance may be extended to other cereal crops after optimizing the genetic background and effects of agro-climatic conditions on safener chemistry, concentration, and proper combination of seed-applied safeners.