Effect of plant bioregulators on growth, yield and water production functions of sorghum [Sorghum bicolor (L.) Moench]

Use of plant bioregulators has been shown to mitigate the impacts of water stress and benefit crops under water scarce conditions. Therefore, a field experiment was conducted to evaluate the interactive effects of plant bioregulators (PBR's) and supplemental irrigation on growth and grain yield of sorghum [Sorghum bicolor (L.) Moench]. Exogenous application of PBR's included: 10 μM salicylic acid (SA), 100 mg L−1 sodium benzoate (SB), 500 ppm thiourea (TU), 1.5% potassium nitrate (KNO3) at seedling elongation (20 DAS), reproductive (50 DAS) and panicle emergence (75 DAS) stages and control (no spray of PBR). Line source sprinkler system (LSS) was used to apply variable quantities of irrigation water (IW) i.e. equalling 0.95, 0.80, 0.65, 0.50, 0.35, 0.20 and 0.05 times the CPE (cumulative open pan evaporation). The maximum grain yield (3.60-3.88 Mg ha−1) was obtained at IW: CPE 0.80 and declined @ 0.43-0.49 Mg ha−1 for every 0.1 IW: CPE for PBR's and the corresponding values were 3.49 and 0.53 Mg ha−1 without PBR. The application of PBR's mitigated water stress and improved gain yield by 6.8-18.5%. SA was more effective under moderate (IW: CPE 0.79-0.50) while SB and TU were better under severe water deficits (IW: CPE 0.49-0.05). PBR's maintained higher leaf water content, lower canopy temperature, modulated the stomatal opening and ultimately the source-sink relations thereby improving the yield and water productivity under deficit irrigation. The maxima of water productivity varied between 1.16-1.41 kg m−3 with PBR's while it was 1.12 kg m−3 without PBR and the latter could be achieved with 25.2-49.7% lesser irrigation water (IW) with PBR's. It is concluded that PBR's like SB and TU present viable option for improving sorghum yield and water productivity under the conditions of deficit irrigation.