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Drought-tolerant ( DT) maize ( Zea mays L.) hybrids have potential to increase yield under drought conditions. However, little information is known about the physiological determinations of yield in DT hybrids. Our objective was to assess radiation-use efficiency ( RUE), biomass production, and yield in two hybrids differing in drought tolerance. Field experiments were conducted in 2013 and 2014 with two hybrids, P1151 HR ( DT hybrid) and 33D49 (conventional hybrid) under well-watered (I100) and drought (I50) conditions. I100 and I50 refer to 100 % and 50 % evapotranspiration requirement, respectively. On average, P1151 HR yielded 11-27 % greater than 33D49 at I100 and about 40 % greater at I50, At I100, greater yield in P1151 HR was due to greater biomass at physiological maturity ( BMpm) resulting from greater post-silking biomass accumulation ( BMpost). At I50, both hybrids had similar BMpm but P1151 HR showed a higher harvest index and greater BMpost. RUE differed significantly (P < 0.05) between the hybrids at I100, but not at I50. At I100, the RUE values for P1151 HR and 33D49 were 4.87 and 4.28 g MJ−1 in 2013, and 3.71 and 3.48 g MJ−1 in 2014. At I50, the mean RUE was 3.89 g MJ−1 in 2013 and 3.16 g MJ−1 in 2014. Results indicate that BMpost is important for maintaining high yield in DT maize. [ABSTRACT FROM AUTHOR]