Growth and genome-wide association analyses of 100 field-grown barley genotypes exposed to future CO2 concentrations

The continuing increase in atmospheric CO2 concentration will have direct implications for plant growth and agricultural ecosystems, as CO2 is the most important resource for plant growth. Growth and yield of C3 crops are known to be positively affected by elevated CO2. Although recent evidence from studies with a small number of genotypes suggest that intraspecific variability exists among genotypes, a systematic evaluation of a broader set of diverse genotypes under field conditions is still lacking. However, sufficient genetic variation is a prerequisite that would allow breeders to select for CO2 responsiveness. Results of a 2-years field experiment are presented during which a diversity set consisting of 100 barley genotypes was exposed in open-top field chambers to ambient CO2 (~400 ppm) and elevated CO2 (~700 ppm) during the growing seasons. Elevated CO2 increased yield and above-ground biomass by ~18 % and 16 %, respectively, averaged over years and genotypes. However, there were significant differences between genotypes with some genotypes showing a much larger growth response to elevated CO2, indicating a high genetic variability in CO2 responsiveness in barley. A significant difference was observed in the growth and yield responses between 2-rowed and 6-rowed genotypes, such that growth stimulation by CO2 was higher in 6-rowed genotypes than in 2-rowed genotypes. The variability among the cultivars within the diversity set points to the fact that no indirect selection of CO2 responsiveness has been conducted so far in barley. Whole genome-wide association analyses were performed to detect genomic regions involved in the response to elevated CO2, using a QK mixed model approach. Based on 3842 polymorphic mapped SNPs from the Illumina 9k-chip and phenotypic data obtained during the two growing seasons, a total of 134 highly associated (-log p values >3) markers were detected of which 75 were associated with multiple traits.