Respiration and Its Relationship to Germination, Emergence, and Early Growth Under Cool Temperatures in Sorghum

Sorghum [ Sorghum bicolor (L.) Moench] is generally not cold tolerant. Enhanced germination and emergence at low temperatures would facilitate early planting and adaptation to cooler regions due to latitude or elevation. This study examined the relationship between respiration, germination, elongation, and early seedling growth, with a view toward evaluating respiration as a selection trait for improved cold tolerance in sorghum. Germination, elongation, seedling fresh wt., and O 2 uptake of 12 cultivars from different genetic backgrounds were measured at temperatures from 5 to 30°C. For most cultivars, the rates of germination and elongation were positively and linearly correlated with O 2 uptake. Other cultivars showed a plateau of germination rates at around 25°C even though respiration continued to increase at higher temperatures. Cultivars from high elevations in Ethiopia and Rwanda had the greatest respiration, germination, and elongation rates, and those from Egypt had the smallest. Factor analysis showed that germination and elongation rates were not strongly associated with shoot and root fresh wt., but respiration was associated with all variables. Respiration rates measured at 10 and 15°C had the highest association with germination and elongation rates, while respiration at 25°C was associated with seedling growth characteristics. Our study suggests that respiration can serve as a useful selection criterion for early cold tolerance in sorghum.