Iodine as a Heat Stress Mitigator During the Flowering Phase in Maize Plants

Iodine is a non-essential element for plants, yet recent studies have shown that it plays a role in mitigating abiotic stress. Heat stress (HS) and water stress (WS) impair maize growth and development, especially during the reproductive phase. This study evaluated whether iodine applications could mitigate HS and combined HS + WS during maize flowering. The experiment was conducted under greenhouse conditions, growing maize plants in pots containing 3 kg of Oxisol. Treatments included foliar or soil applications of iodine under two stress conditions (HS and HS + WS). Iodine was applied to the soil via top dressing and as a foliar application at the start of flowering. On the last day of stress, chlorophyll levels, specific enzyme activity, compatible osmotic solutes, relative water content (RWC), and Fv:Fm (photosynthetic quantum efficiency) were measured. Grain yield was determined at the end of the crop. There was no mitigation of stress with iodine application under combined stress (HS + WS). Under HS, foliar application of iodine, compared with no iodine application mitigated stress, increasing Fv:Fm by 58% (values of 0.73 for foliar iodine application versus 0.02 for no iodine application), RWC by 83% (values of 99% for foliar iodine application), and grain yield by 35%, along with higher levels of chlorophyll a (+28%), chlorophyll b (+73%), total chlorophyll (+31%), and superoxide dismutase activity (SOD). This was also associated with a reduction in sucrose, reducing sugars, total soluble sugars, and total free amino acids. This increase in chlorophyll levels suggests greater photosynthetic capacity, while the higher SOD activity indicates a strengthened antioxidant system under HS. These mechanisms together maintain carbon assimilation and reproductive development, thereby increasing grain yield. Thus, it was concluded that iodine could help reduce HS effects during maize flowering.