Functional Traits of Olive Varieties and Their Relationship with the Tolerance Level towards Verticillium Wilt

Abstract

Verticillium wilt of olive (VWO), caused by the soil-borne pathogen Verticillium dahliae, is considered one of the most important diseases affecting this tree crop. One of the best VWO management measures is the use of tolerant cultivars. Remarkably, no information is available about olive functional traits and their potential relationship with tolerance to V. dahliae. Twenty-five selected functional traits (for leaf, stem, root and whole plant) were evaluated in six olive varieties differing in their VWO tolerance level to identify possible links between this phenotype and functional traits' variation. High intervarietal diversity was found among cultivars and several functional traits were related with VWO tolerance. Tolerant varieties showed higher leaf area, dry matter content (leaf, stem and plant) and mass fraction for stems, but lower for leaves. Significant differences were also detected for root functional traits, tolerant cultivars displaying larger fine root diameter and lignin content but smaller specific length and area of thick and fine roots. Correlations were found among functional traits both within varieties and between levels of tolerance/susceptibility to VWO. Associations were observed between biomass allocation, dry matter content and VWO tolerance. The most relevant difference between tolerant and susceptible cultivars was related to root system architecture.

Keywords: SRA (specific root area); SRL (specific root length); Verticillium dahliae; biomass allocation; breeding for resistance; dry matter content; leaf area; lignin; root architecture.

Figure 1

Boxplots showing median values of Area (‘leaf area’) (A), LMA (‘Leaf mass per area’) (B), LDMC (‘Leaf dry matter content’) (C) and SDMC (‘Stem dry matter content’) (D). Tolerant cultivars are represented in green color while the susceptible ones are shown in purple color. Letters indicate Tukey HSD post hoc tests at the p < 0.05 level, following ANOVA.

Figure 2

Principal Component Analysis (PCA) of leaf (A), root (B) and plant (C) traits performed with ‘tolerance’ as factor, and the contribution of variables on the main two axes of PCA. Different letters (a or b) indicate significant differences between groups (Tukey test, p < 0.05). Leaf traits: ‘Area’, LDMC (‘Leaf dry matter content’), L/W (‘Length/Width ratio’), LMA (‘Leaf mass per area’) and ‘Perimeter’. Root traits: RDMC (‘Root dry matter content’), SRL (‘Specific root length’) and AvgDiam (‘Diameter’) for fine and thick roots, ‘Total lignin content’ and AIR (‘Acid insoluble residue’). Plant traits: PDMC (‘Plant dry matter content’), LMF (‘Leaf mass fraction’), SMF (‘Stem mass fraction’) and RMF (‘Root mass fraction’).

Figure 3

Boxplots showing median values of the ANOVA analysis of the most statistically significant root traits: SRA Thick Root (‘Thick root specific area’) (A), SRL Thick Root (‘Thick root specific length’) (B), ASL (‘Acid soluble lignin’) (C) and ‘Total lignin content’ (D). Tolerant cultivars are represented in green color while the susceptible ones are shown in purple color. Letters indicate Tukey HSD post hoc tests at the p < 0.05 level, following ANOVA.

Figure 4

Boxplots showing median values of the ANOVA analysis of the most statistically significant plant traits: PDMC (‘Plant dry matter content’) (A), LMF (‘Leaf mass fraction’) (B) SMF (‘Stem mass fraction’) (C). Tolerant cultivars are represented in green color while the susceptible ones are shown in purple color. Letters indicate Tukey HSD post hoc tests at the p < 0.05 level, following ANOVA.

Figure 5

Bivariate correlation matrix between functional traits of the six olive varieties (Empeltre, Frantoio, Picual, Hojiblanca, Nevado fino y Lechín de Sevilla) here under study. Left and right ellipse inclination indicate significant negative and positive correlation, respectively. Blue and red colors indicate significant positive and negative correlations, respectively (p < 0.05). A high correlation coefficient is indicated with thin ellipses. Black squares group all functional traits of a specific plant organ (i.e., root, leaf and the entire plant) or trait (i.e., lignin content). Green and yellow squares group the functional traits for fine and thick roots, respectively.