Silicon seed inoculation enhances antioxidants, physiology and yield of hybrid maize under heat stress.

Background: Heat stress, next to drought, is one of the major constraints to maize crop growth, development and sustainable yield in the tropics and sub-tropics, particularly in arid and semi-arid climatic regions. Hence, there is a dire need to explore strategies that alleviate adverse effects of heat stress. In this regard, silicon (Si) is an important plant nutrient which may support crop in alleviating heat stress-induced damages by modulating plant defense mechanisms. The aim of the study was to explore the potential role of Si for inducing heat tolerance in hybrid maize. Yet, to date, limited knowledge is available on how Si modulates plant defense mechanisms to induce heat tolerance in maize crop.

Methods: Two maize hybrids were adopted for field experiment (heat tolerant and sensitive selected from a pot experiment study) on the basis of traits performance through screening in the glasshouse. Six maize hybrids were tested at different heat stress levels (T₁ = control; T₂ = 40 °C ± 3 and T₃ = 45 °C ± 3 for a period of 6 h per day) at six leaf growth stage (V6) in the glasshouse. Secondly, a field experiment was conducted to evaluate the effect of Si seed inoculation [Si₀ = 0.0 mM (control); Si₁ = 3.0 mM (recommended); Si₂ = 6.0 mM] on physiology, growth, antioxidants activity and yield traits of two selected maize hybrids; H₁ = AA-9633 (heat sensitive); H₂ = YH-5427 (heat tolerant) under heat stress conditions (HS₀ = control (without heat stress); HS₁ = heat stress at pollination stage- 65 days after sowing for a period of 8 consecutive days).

Results: The field study results showed that maize hybrid "YH-5427", a prior rated as heat tolerant, produced higher cob length, number of grains per cob, thousand grain weight and grain yield through improved photosynthetic rate, stomatal conductance, water use efficiency, activity of superoxide dismutase, peroxidase and catalase with the seed inoculation of Si (6.0 mM) under heat stress conditions. However, heat sensitive hybrid (AA-9633) produced reduced grain yield (9.26%) and yield components as attained by YH-5427 with the seed inoculation of Si (6.0 mM) under heat stress conditions.

Conclusion: Maize hybrid YH-5427 with Si seed inoculation (6 mM) is a promising option to maintain relatively high maize grain yield (t ha^- 1) under heat stress conditions.