Relating Freeze-induced Electrolyte Leakage Measurements to Lethal Temperature in Red Raspberry

Abstract

Seasonal cold hardiness of red raspberry ( Rubus idaeus L.) canes was measured by freeze-induced electrolyte leakage test and visual rating of injury. Leakage data were transformed to percentage-adjusted injury values and related to lethal temperature by graphical interpolation and by the midpoint (T 50 ) and inflection point (T max ) estimates derived from three sigmoid (the logistic, Richards, and Gompertz) functions. T max estimates produced by Richards and Gompertz functions were corrected further using two different procedures. The 10 leakage-based hardiness indices, thus derived, were compared to lethal-temperature estimates based on visual rating. Graphical interpolation and T max of the logistic or T 50 of the Gompertz function yielded lethal-temperature estimates closest to those obtained visually. Also, T max values of the Gompertz function were well correlated with visual hardiness indices. The Richards function yielded hardiness estimates deviating largely from visual rating. In addition, the Richards function displayed a considerable lack of fit in several data sets. The Gompertz function was preferred to the logistic one as it allows for asymmetry in leakage response. Percentage-adjusted injury data transformation facilitated curve-fitting and enabled calculation of T 50 estimates.