Investigations on the chemical composition of cuticular waxes in twelve Fragaria L. genotypes

Cuticular waxes play an important role in the defence system of plants. To date, reports on the chemistry of waxes from the genus Fragaria L. are very scarce and only related to the cultivated strawberry F. xananassa. In this study, the chemical composition of cuticular waxes in different genotypes of strawberries are described for the first time extensively. Cuticular waxes were then extracted separately from the ad-and abaxial surfaces of fully developed and pathogen free leaves from greenhouse cultivation using chloroform as an apolar organic solvent. Additionally, for adaxial surfaces the epi-and intracuticular wax layers were analysed separately. The quantitative composition was studied by gas chromatography (GC) with flame ionisation detection and single compounds were identified by coupled GC-mass spectrometry. Substantial differences in total mass and relative composition between the ab- and adaxial leaf sides and between different genotypes were detected with alkanes, fatty acid alkyl esters and aldehydes representing major compound classes. Other aliphatic compounds, triterpenoids and non-identified substances were detected only in minor quantities. Additionally, cinnamic acid alkyl esters were found exclusively on adaxial sides whereas secondary alcohols were only present on abaxial sides. Similar differences could be detected between the epi- and intracuticular layer of adaxial leaf surface. The chemistry of cuticular waxes can influence infection processes of pathogens in different ways. Therefore, the obtained results can be used in forthcoming investigations about resistances to fungal, bacterial and animal pathogens.