The temperature effectiveness functions found for this
study generally more closely approximate the exponential
´function of Bidabe (1967) and Lantin (1973) than the more
conventional chill units where the temperature factor is
assumed constant over a range of temperatures (Sunley et al.
2006). For all the genotypes used in this study, the effective-
ness of chilling increases as temperature falls to 0 °C and in
most cases even below (especially ‘Ben Gairn’, ‘Ben Starav’
and ‘Ben Tirran’). An important result from the present data,
however, is the demonstration that the most appropriate
temperature function depends on the model used for temper-
ature accumulation over time (Fig. 5). Furthermore, there is
clearly also an interaction between the temperature response
function that is appropriate for any cultivar and the length of
low-temperature exposure (Fig. 6). The ability to separate
germplasm on the basis of optimal chilling temperature can
enable the selection of appropriate cultivars for specific