Geographical and within-population variation of constitutive chemical defences in a Mediterranean oak (Quercus ilex)

Abstract

Aim of study: to assess whether constitutive levels of total phenols and condensed tannins acting as chemical defences in Quercus ilex vary across regions, populations and genotypes. Area of study: acorns from six Spanish regions with natural presence of Q. ilex were collected for later sowing in the greenhouse of the University of Extremadura at Plasencia, western Spain. Materials and methods: 1176 acorns from 12 populations (2 per region) were sown according to a nested design (6 regions x 2 populations/region x 7 genotypes/population). After five months, 588 emerged seedlings were harvested for phenol extraction from their leaves. Quantification of total phenols through the Folin-Ciocalteu method and condensed tannins by Porter's reagent method was carried out. Main results: total phenolics and condensed tannins correlated positively. Significant differences were found for the concentration of total phenolics and condensed tannins among regions and among genotypes, but not among populations within regions. The lowest levels of constitutive defences were found in the northern Iberian Peninsula. Also, the defensive phenolic content was significantly higher in regions with acidic soils. Heritability values (total phenols 0.37±0.08 and condensed tannins 0.48±0.36) were lower than those obtained of total tannins in a previous study. Research highlights: constitutive levels of heritable chemical defences in holm oak significantly depend on their geographical origin and genotype. Keywords: condensed tannins, genetic and latitudinal variability, heritability, total phenolics.