Differential thermal analysis, supercooling and cell viability in organs of Olea europaea at subzero temperatures.

Abstract

Cold hardiness in different organs and tissues of four different olive ( Olea europaea L.) cultivars characterised in a previous work as different in frost tolerance, was assessed by four different methods (diffe- rential thermal analysis, visual score, vital stain and electrolyte leakage) to determine which method is more reliable for estimating freezing injury in olive. Results obtained with the different techniques consistently agreed. Among the four different procedures utilised, DTA was by far the fastest, whereas the visual score method the simplest, although not as quantitative as the other three methods. It would appear from the present study that the order of sensitivity in the different organs of olive is secondary roots > primary roots > apical lea- ves > basal leaves > shoots > vegetative buds. 'Ascolana' was the most chilling-tolerant variety, whereas 'Coratina' the most chilling-sensitive. The wide range of tolerance showed by olive (i.e. from -11.2 to -15.3°C for the leaves) together with the recurrent danger of frost in many areas of cultivation, made this species an ideal candidate to breeding for low-temperature-tolerant plants.