Diurnal Chilling Sensitivity and Desiccation in Seedlings of Tomato

Seedlings of six cultivars of tomato ( Lycopersicon esculentum Mill.) showed differences in chilling sensitivity depending on the time during the diurnal light/dark cycle when they were placed at low temperature. In all cultivars, sensitivity was highest when the chilling exposure started at the end of a dark period, although the magnitude of the diurnal variation differed among the cultivars. When roots were removed prior to or just after chilling, injury also appeared earlier in seedlings whose chilling was started at the end of a dark period. Seedlings chilled starting at different times during the diurnal cycle had similar stomatal conductance values during chilling. It appears that diurnal changes in chilling sensitivity are not due to altered root function during or following chilling exposure, nor to variations in desiccation during the chilling period resulting from diurnal differences in stomatal conductance.