Host responses to natural infection by Cytonaema sp. in the aerial bark of Eucalyptus globulus

Abstract

The chemical and anatomical host responses to natural fungal infection by Cytonaema sp. in the aerial bark of 3-year-old Eucalyptus globulus plantation trees were examined. The lesion margin (LM) of the canker-infected bark was characterized by the formation of a layer of dark extractives visible to the naked eye. Chemical analysis of the LM by gas chromatography-mass spectrometry (GC-MS), highperformance liquid chromatography (HPLC) with ultraviolet detection and HPLC-MS using negative ion electrospray ionisation indicated the presence of a range of compounds including hydrolysable tannins, polymeric proanthocyanidins, flavonoid glycosides, formlyated phloroglucinol compounds and volatile terpenes. These compounds were either undetectable in healthy tissue or present at significantly lower concentrations than in the LM. The LM of the canker-infected bark was morphologically distinct from healthy phloem, its characteristics varying depending on severity of canker infection. In superficial infections in which only the phloem was affected, the following LMs were observed: (i) a continuous wound periderm of multiple layers, or (ii) an incompletely differentiated and discontinuous wound periderm. In cases of severe canker infections in which the vascular cambium had been killed, the new phloem formed subsequently contained traumatic oil glands in addition to the responses observed for superficial canker infections. All LMs were characterized by the formation of new parenchyma cells that stained positive for the presence of polyphenols. The significance of the chemical and structural responses as defence mechanisms against fungi causing stem canker is discussed.

Performance of Sirex noctilio ’s biocontrol agent Deladenus siricidicola , in known and predicted hosts

“…Further samples of ground sapwood used in the petri dish bioassays were taken, and approximately equal amounts of the coarse (1.004 ± 1.0 Â 10 À3 g) and fine (1.004 ± 1.3 Â 10 À3 g) samples were mixed together and extracted in dichloromehane (Ajax, 10 mL) for 48 h in the dark at 4°C (after Cadahia et al, 1997;Eyles et al, 2003;Hayes et al, 2014). Samples were stored in the freezer until analysis.…”

Corymbia phloem phenolics, tannins and terpenoids: interactions with a cerambycid borer

“…Samples were ground individually with a coffee grinder (Braun), sub-samples of which (230-250 mg) were then extracted in 1.5 mL of 70 % aqueous acetone for 48 h in darkness at 4°C (after Eyles et al 2003). Solvent was removed by air-drying at ambient temperature, followed by drying under a stream of N 2 at 40°C then under high vacuum.…”

“…Further sub-samples of the ground bark samples (230-250 mg) were extracted in methanol (1 mL) for 48 h in the dark at 4°C (after Cadahia et al 1997;Eyles et al 2003). Samples were then stored in the freezer until analysis.…”

“…Inducible defences, on the other hand, are triggered by insect or pathogen invasion and include formation of necrotic tissue that confines the invader (Paine et al 1988) and increased levels of chemicals, to deter establishment and further attack (e.g. Eyles et al 2003). It is widely believed that the best explanation for intraspecific differences in host plant susceptibility to herbivory or pathogenic attack is variations in the chemistry of the host plant (Zangerl and Berenbaum 1993).…”

Constitutive or induced defences - how does Eucalyptus globulus defend itself from larval feeding?

“…However, although changes in plant secondary metabolites have been recorded as a response to, for example, wounding and disease in the phloem and xylem of eucalypts (Eyles et al 2003a;2003b), induced responses as a result of foliarchewing insect herbivory have yet to be demonstrated (Haukioja et al 1994). Nevertheless, Edwards and Wanjura (1989) have reported that several species of eucalypt feeding insects chew off and discard partially eaten leaves and proposed that these insects are sabotaging a feedback loop from the damaged leaf to the host tree that may confer resistance.…”