Effects Of The Foliar-applied Salicylic Acid,Zinc,and Glycine Betaine In Improving Drought-tolerance Of Wheat And Maize During Critical Growth Stages

Drought has become a dangerous threat to reduce crop production throughout the world.The exogenous applications of regulators,micronutrients,and osmoprotectants in foliar inducing drought-tolerance are typically and intensively adopted.Two controlled pot experiments were conducted at the glasshouse of the Experimental Farm,Southwest University,China,in a complete randomized design to investigate the relative efficacy of salicylic acid(SA),zinc(Zn),and glycine betaine(GB)foliar applications on the growth,leaves pigments contents,relative water content(RWC),leaf gas-exchange attributes,activities of antioxidant enzymes,reactive oxygen species(ROS)accumulation,osmolytes accumulation,yield,and its attributes in wheat and maize plants exposed to drought stress during critical growth stages.The results were as follows:(1)Water stress significantly decreased the growth,yield,yield attributes,RWC,photosynthesis pigment,and gas-exchange attributes except for the intercellular CO₂concentration.However,the foliar applications remarkably improved these parameters under the water-stressed condition.Under the water-stressed condition,the exogenous applications of SA,Zn,and GB increased the dry weight by 15.82%,9.34%and 28.30%,and grain yield by 27.99%,15.23%and 37.36%in wheat,respectively;while they increased the dry weight by 14.31%,12.28%and 22.55%,and grain yield by 40.52%,19.98%and 60.49%in maize,respectively,as compared with the control treatment.(2)Water stress statistically increased the contents of hydrogen peroxide(H₂O₂)and superoxide anion radical(O₂^-),and caused the harmful oxidation to lipids in plant cells which could be appraised by an increased the content of malonaldehyde(MDA).However,they were considerably reduced by foliar applications under the water-stressed condition.Under the water-stressed condition,the exogenous applications of SA,Zn,and GB decreased the contents of H₂O₂by 29.33%,23.99%and 26.45%,O₂^-by36.10%,25.26%and 28.97%,and MDA by 29.09%,16.64%and 26.51%in wheat,respectively;while they decreased the contents of H₂O₂by 28.92%,21.18%and 33.81%,O₂^-by 30.43%,21.73%and 26.08%,and MDA by 27.70%,15.13%and 23.01%in maize,respectively,as compared with the control treatment.(3)The activities of all antioxidant enzymes and contents of free proline and soluble sugar were increased in response to the water-stressed condition as well as foliar applications.Overall,the exogenous applications of GB,SA,and Zn improved drought-resistance in plants and decreased ROS accumulation by promoting their scavenging process because of the increase in antioxidant enzymes activity and accumulation of osmolytes.Under the water-stressed condition,the exogenous applications of SA,Zn,and GB increased the activity of ascorbate peroxidase(APX)by 47.82%,29.89%and42.39%,glutathione reductase(GR)by 59.62%,42.85%and 48.44%,peroxidase(POD)by 26.08%,18.84%and 35.30%,catalase(CAT)by 62.16%,50.95%and 120.11%,and superoxide dismutase(SOD)by 61.42%,34.64%and 42.20%in wheat,respectively;while they increased the activity of APX by 91.89%,42.56%and 74.32%,GR by125.64%,79.48%and 115.38%,POD by 25.16%,14.63%and 33.91%,CAT by30.23%,21.80%and 44.54%,and SOD by 23.54%,10.06%and 14.17%in maize,respectively,as compared with the control treatment.In conclusion,the evidence of the present two controlled experiments showed that the foliar applications of SA,Zn,and GB enhanced the drought-tolerance in wheat and maize crops.Generally,in most assessed parameters,GB treatment was the most effective and followed by SA and Zn applications to alleviate the adverse effects in both crops triggered by drought stress.Finally,these applications could be recommended to the cultivators as effective compounds for increasing the production of wheat and maize crops under drought stress.