Towards Understanding Heat Stress Tolerance of Maize in the Tropics.

Heat stress is a prominent and growing agricultural concern in many areas of the world, negatively impacting production and productivity of major crops like maize. It is estimated that 1% of grain yield is lost due to premature senescence and death of vegetative and reproductive structures for each degree day above 30 °C (Lobell et al., 2011). In the maize-growing regions of South Asia, daily temperatures are regularly 40 °C and higher during reproduction and impose a significant constraint to plant growth. The Heat Tolerant Maize for Asia (HTMA) project is a public-private alliance funded by USAID under the Feed-the-Future Initiative to develop and deploy heat stress tolerant maize cultivars adapted to the tropics, especially in Bangladesh, India, Nepal and Pakistan; the partners include CIMMYT, Purdue University, DuPont Pioneer, National Agricultural Research Institutions in the four target countries, and selected small-and-medium-enterprise seed companies in South Asia. The HTMA project also seeks to understand the genetic and physiological bases of heat stress tolerance in maize. A genome-wide association study (GWAS) was designed to discover genomic regions associated with heat stress tolerance in maize. The Heat-Tolerance Association Mapping (HTAM) panel includes tropical, subtropical and temperate germplasm that exhibit contrasting heat stress phenotypes. The panel was genotyped and extensively phenotyped at the International Crops Research Institute for the Semi-Arid Tropics located near Hyderabad, India during 2013 and 2014 under heat stress and non-heat stress conditions.  Numerous phenotypes were collected including agronomic performance and biochemical traits such as leaf lipid composition. Preliminary analyses revealed multiple genetic loci that were associated with heat stress tolerance. More than 400 significant single nucleotide polymorphisms (SNPs) over multiple peaks were detected for several leaf lipid species. The GWAS results will assist in identifying molecular markers that can be used for accelerating development of heat stress tolerant maize.