Physio-morphological traits and drought stress responses in three wild Mediterranean taxa of Brassicaceae

Crop wild relatives (CWRs) have extremely relevant roles in biodiversity conservation, in investigating phylogeny and improving abiotic stress tolerance of crop plants. We screened the variability in leaf functional traits of three CWRs of kale crops (Brassica oleracea) from Sicily, Italy, grown in pots under well-watered and drought conditions. Our aim was to highlight traits in the different genotypes of endemic Sicilian threatened taxa. We measured several structural/anatomical traits (stomatal size, density and stomatal pore index—SPI, leaf mass per area—LMA) and leaf functional traits (stomatal conductance—gs, leaf water potential—ΨL, leaf temperature (TL), leaf relative water content—RWC) at pre-dawn and midday of leaves of three wild taxa: B. macrocarpa, B. rupestris subsp. rupestris and B. villosa subsp. bivoniana. Pressure–volume curves were constructed to obtain leaf water potential at turgor loss point (Ψtlp), osmotic potential at full rehydration (Ψπ100), relative water content at turgor loss point (RWCtlp), elastic bulk modulus (εmax) and leaf area specific capacitance at full turgor (Cft*). Several significant differences were found among the taxa: under water deficit, B. macrocarpa had the less negative Ψtlp and showed the smallest ΔΨL between pre-dawn and midday. B. villosa subsp. bivoniana showed the highest SPI and had significantly higher gs under water availability, while under drought it had the most negative ΨL. Each of the taxa investigated possessed traits that confer particular stress tolerance, offer competitive advantage in their natural environment and may be exploited for crop improvement.