Late-Season Drought Tolerance in Maize and Sorghum.

Climate extremes of excess heat, drought and flooding continue to challenge global agriculture and food security.  If modeling studies are accurate, climate variability and drought will be a more prevalent occurrence in the future affecting not only grain yield but also stressing water resources.  It is critical to breed for improved climate resilience in agronomic crops and understand the genetic mechanisms conferring adaptation to water limited environments.

Sorghum is an important crop grown in drought prone environments around the world and an important crop model for studying plant adaptation to water-limited environments.  Sorghum breeders have been successful in developing drought tolerant sorghum hybrids using stay-green as a phenotype.  The ability of annual crop species to delay senescence or “stay-green” throughout the grain filling period has been associated with increased yield, decreased lodging, and stalk rot resistance in sorghum.  Genetic analyses of stay-green in sorghum suggest the trait is controlled by four to six loci that have been integrated into commercial programs by marker-assisted breeding. 

The goal of our research is to characterize the genetic architecture of stay-green in maize.  Maize exhibits substantial genetic variation for stay-green.  We evaluated the Nested Association Mapping (NAM) populations of maize and testcross hybrids with PHZ51 for variation in stay-green in multi-location trials.  Joint linkage mapping was used to identify multiple QTL for stay-green across several linkage groups with sources of stay-green alleles coming from diverse genetic backgrounds.  Comparisons between maize and sorghum for map positions of these stay-green QTL indicate that two of the major loci occur in syntenous regions.  Identification and integration of stay-green genes into commercial programs provides the opportunity to sustainably enhance the productivity of maize and sorghum in drought environments.