A seed respiration-based index of cold sensitivity during imbibition in four macrothermal species

A research was carried out to evaluate the influence of temperature on seed respiration response of maize, cotton, grain sorghum and sunflower during imbibition, and to define reliable indices for a fast evaluation of cold-sensitivity at germination level in plants. The seed respiration activity was measured during seed imbibition at 25°(optimal) and 15°C (suboptimal) constant temperatures, using an home-made respiration chamber adapted to an infrared gas analyser. At 15°C sunflower and sorghum maintained high levels of seed germination (>=90%), whilst this last dropped in cotton (36.7%) and maize (27.8%). To this respect, cotton and maize seem to be cold-sensitive during germination. Instantaneous seed respiration during imbibition vs. temperature or thermal time could not be used as a good indicator for cold tolerance, since the levels of CO2 recorded at 15°C in cotton (higher than the other species) and maize (similar to that of sorghum and sunflower) did not correspond to adequate seed germination. Differently, the rates (b coefficient of linear regressions) of accumulation of CO2 respired at optimal and suboptimal temperature during the first hours imbibition (up to approximately 24 hours from the start of experiment), were significantly different in maize and cotton, whilst they did not differ in sorghum and sunflower. Therefore, the shift between slopes may represent a reliable index for seed cold sensitivity assessment during early germination