Spray of Stress Protective Chemicals Alleviates Cobalt Toxicity on Growth, Water and Nutrients Status of Hybrid Maize (Zea mays L.).

Frequent discharge of cobalt in ionic form (Co2+) during industrial processes is contaminating agricultural soil through the addition of industrial effluent. Cobalt is beneficial element in trace amounts but its higher concentrations in soil severely damage the growth and development of plants. In this two-year study, the pre-selected sublethal level (0.5 mM) concentration of Co2+ was applied in soil to induce toxicity on two elite maize (Zea mays L.) hybrids ('Hycorn11plus' and 'P-1429'). To encounter the toxic effects of selected sub-lethal (0.5 mM) Co2+ level (applied using CoCl2·6H2O), pre-optimized levels of three stress protective chemicals (SPCs) i.e., ascorbic acid (0.5 mM), salicylic acid (0.5 mM) and thiourea (1.0 mM) were foliar sprayed. The Co2+ and SCPs treatments were applied 10 days after seedling emergence. After ten days of treatment application, the data were recorded for the growth, nutrients and leaf water status. The shoot and root dry weights and shoot-to-root (S/R) ratio were substantially reduced by the Co2+ stress. Co2+ intoxication also enhanced the leaf water loss (LWL) while relative water contents (RWC) were reduced in Co2+ stressed plants. The Co2+ treatment reduced the intake of nitrate-N, sulfate-S, phosphate-P, K+, Ca2+, Mg2+, Zn2+, and Fe2+ contents significantly both in the shoot and root. However, from the correlation matrix, it was noted that the foliar spray of SPCs effectively alleviated the Co2+damage by preventing the influx of Co2+ ions and enhanced the growth, water and nutrient contents except for LWL. From the reduced RWC and shoot and root nutrient contents, as well as increased LWL and Co2+ contents, it is evident that Co2+ interfered with either the function or structure of water and ion-transport systems located on the plasma lemma and tonoplast of root cells. AsA was more effective among the foliar applied SPCs due to its multiple metabolic roles in plants. The foliar spray of SPCs improved the root mass and tendency to absorb essential nutrients under Co2+toxicity indicating an intimate communication between shoot and root. The use of SPCs at the selected levels is a pragmatic strategy to counteract the Co2+ damage to maize in the marginally contaminated areas. [ABSTRACT FROM AUTHOR]