Disaggregating sorghum yield reductions under warming scenarios exposes narrow genetic diversity in US breeding programs

Significance Sorghum’s ability to withstand harsh environmental conditions has placed it in the forefront of discussions regarding potential adaptation paths under climate change. While sorghum may indeed be a good candidate to substitute for other major row crops as warming materializes in areas where it has not traditionally been grown, an equally important consideration is whether its production can be sustained in the warmer areas where it has traditionally been grown. Our findings suggest limited potential for climate change adaption using currently available cultivars but do not preclude the overall role of genetic innovation and enhanced decision making in adapting to climate change. Successful adaptation could perhaps best be facilitated by expanding the scope of genetic stock within sorghum breeding programs. Historical adaptation of sorghum production to arid and semiarid conditions has provided promise regarding its sustained productivity under future warming scenarios. Using Kansas field-trial sorghum data collected from 1985 to 2014 and spanning 408 hybrid cultivars, we show that sorghum productivity under increasing warming scenarios breaks down. Through extensive regression modeling, we identify a temperature threshold of 33 °C, beyond which yields start to decline. We show that this decline is robust across both field-trial and on-farm data. Moderate and higher warming scenarios of 2 °C and 4 °C resulted in roughly 17% and 44% yield reductions, respectively. The average reduction across warming scenarios from 1 to 5 °C is 10% per degree Celsius. Breeding efforts over the last few decades have developed high-yielding cultivars with considerable variability in heat resilience, but even the most tolerant cultivars did not offer much resilience to warming temperatures. This outcome points to two concerns regarding adaption to global warming, the first being that adaptation will not be as simple as producers’ switching among currently available cultivars and the second being that there is currently narrow genetic diversity for heat resilience in US breeding programs. Using observed flowering dates and disaggregating heat-stress impacts, both pre- and postflowering stages were identified to be equally important for overall yields. These findings suggest the adaptation potential for sorghum under climate change would be greatly facilitated by introducing wider genetic diversity for heat resilience into ongoing breeding programs, and that there should be additional efforts to improve resilience during the preflowering phase.