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Temperature Effects on Dark Respiration Among Diverse Sorghum Genotypes¹

Dark respiration is a key physiological process of plant growth and maintenance, but information is limited regarding its genetic variability in grain sorghum. The objectives of this study were i) to determine the range of variability for genetically diverse grain sorghum [Sorghum bicolor (L.) moench] lines and hybrids over a range of temperatures, and ii) to characterize the relationship between dark respiration of a plant during vegetative development and a panicle during grain filling. Dark respiration rates of shoots were determined under controlled conditions at temperatures ranging from 13 to 40°C. At 23°C, the mean rate of dark respiration was 27 µmol CO₂ kg^–1 s^–1 with a range of 32 µmol CO₂ kg^–1 s^–1. Plant growth at near optimum temperatures (30/25°C; day/night) was correlated with dark respiration rates (measured at 29°C) when the rates were expressed on a per shoot basis, but not when expressed on a dry weight basis. Genotypes differed in their sensitivity to temperature. for the genotypes studied, the linear regression coefficients of dark respiration on temperature ranged from 1.1 to 2.5 µmol CO₂ kg^–1 s^–1 °C^–1 over the 13 to 40°C range. Within the limits of this experiment, there appears to be sufficient variability to select high and low respiring grain sorghum genotypes and to distinguish those which possess high or low sensitivity to temperature. Panicle dark respiration rates were 50% lower than those of the vegetative portion of the plant. Both panicle and vegetative shoot dark respiration responded in a linear manner to temperature from 13 to 40°C. The panicle dark respiration increased at a rate of 0.75 µmol CO₂ kg^–1 s^–1 °C^–1 compared with 1.5 for the vegetative shoot indicating that panicle dark respiration was less sensitive to temperature than was shoot dark respiration. This may be related to the linear nature of dry matter accumulation in grain sorghum panicles grown under divergent temperature environments.

Key Words: Genetic variability • Grain filling • Panicle development • temperature sensitivity

² Formerly, graduate research assistant, Univ. of Nebraska, presently, assistant professor, Texas Agric. Exp. Stn., Temple, TX 76503, and professor, Univ. of Nebraska, Lincoln, NE 68583.