Genetic Enhancement of Heat Tolerance in Maize Through Conventional and Modern Strategies

Globally, maize is an important crop and serves as a livelihood for millions of marginal farmers across South Asia and sub-Saharan Africa. However, heat stress has become a globally prominent and growing concern for maize farmers, owing to its adverse impact on maize growth and productivity. In addition, the mean maximum temperature may increase by 2.1–2.6°C in 2050, with significant temporal and spatial variations, across South Asia. Further, the heat-stressed areas would increase to 21% from the current baseline. Heat stress is known to induce a series of morphophysiological, anatomical and molecular changes in maize, thereby affecting growth and development, which ultimately leads to a drastic reduction in the grain yield. Regulation of osmoprotectants, detoxification of excess reactive oxygen species (ROS), expression of heat-responsive/shock genes, and change of plant phenology help in the development of heat tolerance. The molecular basis of heat stress tolerance mechanisms has been appreciably understood and updated using the innovative physiological and molecular tools. Further, functional genomics strategies resulted in the identification of genes and regulatory pathways involved in heat stress tolerance in maize. Several attempts have been made in breeding heat-tolerant maize cultivars. The availability of genomic resources, accessibility to sequence information and millions of SNP markers in maize facilitated the selection for heat tolerance at the genome-level. Genomics-assisted mapping revealed several QTL and interactions for heat stress functional adaptive traits. The new breeding approaches like doubled haploid inducers, genome editing tools and high throughput phenomics at the breeders' disposal are opening up a new era in maize breeding for development of heat resilient maize hybrids.

Keywords: Climate Change, Functional Genomics, Genomics-Assisted Breeding, Heat, Maize, Resilience.