Considering the increase in average earth’s surface air temperature and CO2 concentration during the past decades, an experiment was performed to study the dry matter accumulation as well as partitioning patterns between above and below ground organs in sesame genotypes (I. S., Oltan, and Naaz) under three temperature regimes (33/21, 35.5/23.5, and 38/26 °C day/night) and two concentrations of CO2 (400 and 700 ppm). Results indicated a significant difference among genotypes with respect to root (R), shoot (S), and total dry matter (TDM) genotypes as well as R/S and R/TDM. Both temperature and CO2 concentration had significant effects on the above characters. Increasing temperature increased TDM in genotypes, so that highest TDM was recorded for genotype Oltan under 38/26 °C day/night (19.3 g/plant). Under both CO2 concentrations, increasing temperature resulted in increased R. Total Dry Matter (TDM) and R followed a logistic model in the experiment. Based on the results, 700 ppm CO2 concentration increased R in all genotypes. Genotype Oltan had the highest R under 700 ppm CO2 concentration at 35.5/23.5 °C day/night. According to the results, a period between 22 and 83 Days After Planting (DAP) was critical for R accumulation in response to temperature × CO2 concentration interaction. Increasing CO2 concentration not only increased R/S, but also increased the minimum effective temperature for R/S. Minimum R/TDM was 5.75%, recorded for genotype Naaz in 33/21 °C under 400 ppm CO2 concentration. Increasing CO2 concentration delayed decrease of R/TDM after reaching its peak. This means that higher CO2 concentration maintained CH2O translocation for a longer period.
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