Maintaining grain number by reducing grain abortion is the key to improve water use efficiency of maize under deficit irrigation and salt stress

Drought and soil salinization are threatening maize production in Northwest China, and climate change is exacerbating water shortages. The objective of this study is to explore the mechanisms underlying spring maize yield and water use efficiency under water deficit and salt stress, to coordinate water conservation and maize production. A three-year field trial was conducted with two water levels (full irrigation and deficit irrigation) and two salt levels (0.65‰ and 2‰) using two maize genotypes (ZD958 and XY335). Leaf area, leaf photosynthesis, dry matter accumulation, floret number, grain abortion, ear characteristics and water use efficiency were evaluated. Water, salt and their combined stress significantly decreased the grain yield by 7.3%, 20.5%, and 38.7%, respectively, 93.6% of which was explained by grain number depending on spikelet differentiation. Grain abortion was identified as the primary reason for maize yield reduction under water and salt stress. The reduction in total biomass, rather than biomass allocation suppressed spikelet differentiation under water and salt stress. Water or salt single stress improved water use efficiency (3.7%–17.5%) by reducing evaporation compared with no stress. Furthermore, water and salt combined stress significantly decreased maize productivity leading to reduction in water use efficiency. Taken together, reducing grain abortion to maintain grain number is the key to alleviate maize yield loss and improve water use efficiency under water and salt stress.