Internal Resistance in Winter Oilseed Rape Inhibits Systemic Spread of the Vascular Pathogen Verticillium longisporum

Abstract

Verticillium longisporum is a vascular fungal pathogen presently threatening oilseed rape production in Europe. Systemic spread and vascular responses were studied in a susceptible ('Falcon') and a resistant genotype (SEM 05-500256) of Brassica napus. Colonization of both genotypes after dip-inoculation of the roots followed by quantitative polymerase chain reaction revealed similarities only in the initial stages of root penetration and colonization of the hypocotyl, while a substantial invasion of the shoot was only recorded in 'Falcon'. It is concluded that the type of resistance represented in SEM 05-500256 does not prevent the plant base from being invaded as it is internally expressed well after root penetration and colonization of the plant base. The morphological and biochemical nature of barriers induced in the hypocotyl tissue upon infection was studied with histochemical methods accompanied by biochemical analyses. Histochemical studies revealed the build-up of vascular occlusions and the reinforcement of tracheary elements through the deposition of cell wall-bound phenolics and lignin. Furthermore, the accumulation of soluble phenolics was observed. Although these responses were found in vascular tissues of both genotypes, they occurred with a significantly higher intensity in the resistant genotype and corresponded with the disease phenotype. In the resistant genotype phenols were differentially expressed in a time-dependent manner with preformed soluble and cell wall-bound phenolics at earlier time points and de novo formation of lignin and lignin-like polymers at later stages of infection. This is the first study identifying a crucial role of phenol metabolism in internal defense of B. napus against V. longisporum and locating the crucial defense responses in the plant hypocotyl.

Verticillium longisporum Infection Affects the Leaf Apoplastic Proteome, Metabolome, and Cell Wall Properties in Arabidopsis thaliana

“…Studies comparing resistant and susceptible cultivars of pepper, cotton, cauliflower, broccoli and tomato provided evidence that peroxidases and increased lignification are involved in the defense against V. dahliae and V. albo-atrum [21], [54]–[58]. Similarly, Eynck et al [59] found that cell wall re-inforcement and lignification in the hypocotyl limited the spread of V. longisporum in a resistant cultivar of B. napus , although the fungus was able to colonize the roots of both cultivars. Our data indicate that these defenses are also activated in VL-infected Arabidopsis .…”

Potential of Endophytic Fungi Isolated from Cotton Roots for Biological Control against Verticillium Wilt Disease

“…dahlia [47]. Similarly, lignin might be important at later infection stages, whereas the soluble and cell wall-bound phenolics seem to be involved in the early defense against the fungus [48], which could oxidize phenolic compounds into quinones to inhibit pathogen, and improve the resistance of plants.…”

N-Acyl-Homoserine Lactone Primes Plants for Cell Wall Reinforcement and Induces Resistance to Bacterial Pathogens via the Salicylic Acid/Oxylipin Pathway

“…For distal tissues, phenolic compounds were measured in leaves of plants grown for 5 weeks in the sterile systemic hydroponic system, in which roots were pretreated with oxo-C14-HSL for 3 d and leaves subsequently challenged with 1 mM flg22 for 24 h. Samples were taken 0 and 24 h after challenge, freeze-dried, and crushed with metal beads in a TissueLyser. All phenolic compounds were measured via a colorimetric assay based on the Folin-Ciocalteau method (Eynck et al, 2009) with some modifications. The soluble phenolic compounds were extracted twice with 80% aqueous methanol for 1 h. The phenolic compounds were measured in the merged supernatants.…”