Chilling tolerance in maize: Agronomic and physiological approaches

Maize is a C₄ plant species with higher temperature optima than C₃ plant species. Growth and productivity of maize are severely constrained by chilling stress. Here, we review the effects of chilling stress on growth, phenology, water and nutrient relations, anatomy, and photosynthesis in maize. Several management strategies to cope with chilling stress are also proposed. In maize, chilling stress is known to reduce leaf size, stem extension and root proliferation, disturb plant water relations, and impede nutrient uptake. Chilling stress in maize is a complex phenomenon with physiological and biochemical responses at both cellular and whole-organ level. CO₂ assimilation by leaves is reduced mainly due to membrane damage, photoinhibition, and disturbed activity of various enzymes. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on tissues as both processes generate reactive oxygen species (ROS). Injury caused by ROS to macromolecules under chilling stress is one of the major deterrents to growth. Low-molecular-weight osmolytes, including glycinebetaine, proline, and organic acids, are crucial in sustaining cellular function under chilling stress. Plant growth substances such as salicylic acid, gibberellic acid, and abscisic acid modulate the response of maize to chilling stress. Polyamines and several enzymes act as antioxidants and reduce the adverse effects of chilling stress. Chilling tolerance in maize can be managed through the development and selection of chilling-tolerant genotypes by breeding and genomic approaches. Agronomic approaches such as exogenous application of growth hormones and osmoprotectants to seeds or plants, and early vigour, can also aid in chilling tolerance.