S11 - Session O4 - Understanding and manipulating cold tolerance - Breeding for frost resistance in Lavandula spp

Authors: Ewout Van Oost *, Leen Leus, Bert De Rybel, Katrijn Van Laere

Driven by climate change and increasing temperatures, the demand for drought tolerant ornamental plants like lavender is rising in northwestern Europe. Species like Lavandula stoechas and L. dentata therefore become more popular to complement the assortment of ornamental lavender which is now dominated by L. angustifolia . However, these species are commercialized as potted summer annuals because their use as perennial plants is problematic in temperate climates due to insufficient frost resistance. To increase the understanding and facilitate breeding towards frost resistance in lavender, a collection of 37 lavender genotypes comprising 20 different species and hybrids, was used to determine the variability in frost resistance among the genus. This frost resistance screening was performed by measuring the electrolyte leakage of leaf samples after exposure to sub-zero temperatures. Significant differences in frost resistance were detected among species and correlated with frost damage observed under field conditions. For L. angustifolia , frost damage was only observed at -18°C or lower temperatures, while L. dentata and L. stoechas showed considerable frost damage at -8°C. based on the screening, a subset of 6 genotypes ( i.e., 2 frost resistant, 2 frost susceptible and 2 intermediate genotypes) is selected to study the influence of different anatomical, biochemical and physiological parameters on frost resistance. The seasonal fluctuation of proline and water content of the leaf and stem tissue will be evaluated. Also, the anatomy of the vascular tissue will be studied by measuring xylem vessel diameter and lignin content in stem coupes. In addition, genetic relationships, i.e., differences in genome size, chromosome numbers and a phylogenetic tree using AFLP data were studied to evaluate breeding opportunities for interspecific hybridization and to enhance frost resistance. The results in our study will support breeding programs towards the creation of improved Lavandula cultivars for a world in transition.