Quantitative Trait Loci Mapping of Cotton Physiological Traits in Response to Environmental Stress

The long-term sustainability of the U.S. Southwest cotton industry is at risk from global climate change and heightened competition for scarce water resources. The development of high-throughput tools to phenotype physiologically related traits under relevant growing conditions creates the possibility to more efficiently breed superior cotton cultivars that are resilient to environmental stress. In that light, we developed and evaluated a novel, tractor-based phenotyping system that deployed sets of sensors to simultaneously measure canopy reflectance and temperature on a cotton recombinant inbred line mapping population. The evaluation trials were conducted under well-watered and water-limited conditions in a replicated field experiment at Maricopa, Arizona with trait measurements taken at different times on multiple days. Measurements of canopy temperature and normalized difference vegetation index (NDVI) displayed moderate to high levels of heritability as well as expected interactions among genotypes with water regime and time of day. Quantitative trait loci (QTL) mapping was employed to identify differentially expressed QTL in these time-related traits. Expression profiles were monitored over the course of a day as well as the growing season and exhibited variation in relation to water regime and the time of measurement. These results highlight the utility of high-throughput phenotyping platforms to help dissect the genetics of stress-adaptive traits which will facilitate the development of environmentally robust cultivars.