Silicon seed inoculation improves growth, physiological mechanisms, grain and biological yields in maize hybrids under heat stress at vegetative and tasseling stages

Heat stress, next to drought, is one of the major constraints to maize growth, development and sustainable yield in tropical and sub-tropical 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. Si seed inoculation can be an ecofriendly mitigation strategy to ameliorate adverse effects of heat stress in maize. Yet, to date, limited knowledge is available on how Si modulates plant defense mechanisms to induce heat tolerance in maize. Therefore, a consecutive two years field trials were conducted in arid climatic conditions to evaluate the effects of six Si seed inoculation levels (0.00 to 6.00 mM) on the phenological, physiological, growth, antioxidant mechanisms, and yield components of (heat tolerant and heat sensitive) maize hybrids under normal temperature regime and heat stress conditions at the sixth leaf and 50% tasseling growth stages over a period of 8 consecutive days. Previously, the maize hybrids were selected on the basis of traits performance through screening in the glasshouse where hybrids were tested at different heat stress levels at sixth leaf stage-V6. Results showed that when the heat stress was imposed at sixth leaf stage then seed inoculation with 4.5 mM Si produced significant better cob length (15.0 cm, 16.7 cm), grains per cob (480, 500), thousand grains weight (211.6 g, 224.3 g), grain yield (6.58 t ha^-1, 7.11 t ha^-1) and biological yield (13.1 t ha^-1, 14.5 t ha^-1),  respectively for 2023 and 2024 growing seasons (years) as compared to other Si levels. Whereas, the same Si inoculation also produced the maximum cob length, grains per cob, thousand grains weight, grain yield (6.24 t ha^-1, 6.74 t ha^-1) and biological yield (13.7 t ha^-1, 15.2 t ha^-1), respectively for both growing seasons as compared with other Si inoculation when heat stress imposed at 50% tasseling stage. These results owing to increased physiological mechanism, growth, antioxidant activities, and osmolytes accumulation under heat stress conditions. Moreover, the interactive effects of heat stress and hybrids revealed that the maize hybrid DK-6103 (prior defined as heat tolerant) produced more grain yield (6.02 t ha^-1, 6.50 t ha^-1) and biological yield (11.4 t ha^-1, 12.6 t ha^-1), respectively during both years when the heat stress was imposed at six leaf stage. While, hybrid SW-1080 produced on an average 13.5% and 14.8% less grain and biological yields, respectively as attained by DK-6103. Therefore, the Si seed inoculation (4.5 mM) may be good strategy to alleviate the adverse effects of the heat stress in maize hybrids. Future studies are also needed to explore the role of Si in alleviating the adverse impacts of combined drought and heat stress under contrasting environmental conditions.

Keywords: Sixth leaf and tasseling phenological stages, physiological mechanism, antioxidants, grain yield, arid and semi-arid climatic regions