Appraisal of the physio-biochemical efficacy of exogenously applied natural and synthetic sources of plant growth stimulants in modulating drought stress tolerance in maize (Zea mays L.)

Phytoextracts as a cheap source of growth promoters as well as synthetic chemicals are being widely used these days to treat plants subjected to stress conditions. To compare the effects of natural growth regulators and synthetic ones, a pot experiment was conducted using natural [moringa leaf extract (MLE)] and synthetic (vitamins B1 and B2) sources to appraise the mitigating of drought-induced adverse effects on maize (Zea mays L.) plants. Seeds of both differentials stress tolerant maize cultivars (YH-1898 and Sahiwal Gold) were primed with natural (MLE), synthetic (thiamin and riboflavin), and their combination (MLE, thiamin, and riboflavin) and subjected to 100% field capacity [F.C. (control)] and 60% F.C. (drought) conditions. Drought stress (60% F.C.) significantly decreased plant biomass and total soluble proteins (TSP), whereas no significant alteration was observed in chlorophyll contents. However, in contrast, it improved glycine betaine (GB), proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), total phenolics, and ascorbic acid as well as the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) enzymes in both maize cultivars. Priming seeds with different sources enhanced growth attributes, chlorophyll pigments, osmolyte concentration, total phenolics, ascorbic acid, and the activities of reactive oxygen species (ROS) scavenging enzymes (SOD, POD, and CAT), but it reduced the accumulation of H2O2 and MDA. Overall, a natural source, MLE as a plant growth regulator, remarkably reduced the adverse effects of drought stress and enhanced the growth of maize cultivars, whereas riboflavin among the synthetic PGRs was more effective in upregulating the oxidative defense and osmoprotectant accumulation.