Assessing frost tolerance in Lavandula spp. by measuring electrolyte leakage

The use of more diverse lavender (Lavandula spp.) genotypes as perennial ornamentals is limited in temperate regions because of lack of frost tolerance in most species. The ornamental potential in the genus could be further exploited through targeted breeding and selection. To assess frost tolerance in lavender, a standardized assay is needed. Therefore the aim of this study was to optimize the electrolyte leakage method as an objective assessment for frost tolerance screening in lavender. In leaf and stem tissue of six cold-acclimated lavender species electrolyte leakage was measured after a stepwise freezing treatment in a refrigerated bath. The data obtained were used to calculate the indices of injury. A Gompertz dose-response curve was fitted to the indices of injury and the LT₅₀ and T_max were estimated. Our results showed that leaf tissue was more susceptible to frost damage compared to stem tissue. T_max, corresponding with the temperature at which the rate of the injury process is maximum, was preferred over LT₅₀ as an objective estimation of frost tolerance in lavender. Based on the electrolyte leakage data from leaf tissue and derived T_max, differences in frost tolerance could be demonstrated among the six lavender species tested. Results obtained in this study could enhance future breeding and selection of improved Lavandula genotypes toward frost tolerance.