Holm Oak (Quercus ilex subsp. ballota (Desf.) Samp.) Bark Aqueous Ammonia Extract for the Control of Invasive Forest Pathogens

Abstract

Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.) bark is a commonly used remedy to treat gastrointestinal disorders, throat and skin infections, hemorrhages, and dysentery. It has also been previously reported that its methanol extracts possess antibacterial activity, which can be related to the richness of Quercus spp. extracts in phenolic compounds, such as flavonoids and tannins. However, there is no information on the antifungal (including oomycete) properties of the bark from Q. ilex or its subspecies (ilex and ballota). In this work, we report the characterization of the aqueous ammonia extract of its bark by FTIR and GC-MS and the results of in vitro and ex situ inhibition tests against three phytopathogens. The main phytochemical components identified were inositols (19.5%), trans-squalene (13%), 4-butoxy-1-butanol (11.4%), gulopyranose (9.6%), lyxose (6.5%), 2,4-dimethyl-benzo[H]quinoline (5.1%), catechol (4.5%), and methoxyphenols (4.2%). The efficacy of the extract in controlling forest phytopathogens was tested in vitro against Fusarium circinatum (responsible for pitch canker of Pinus spp.), Cryphonectria parasitica (which causes chestnut blight), and Phytophthora cinnamomi (which causes ‘root and crown rot’ in a variety of hosts, including Castanea, conifers, Eucalyptus, Fagus, Juglans, Quercus, etc.), obtaining EC90 values of 322, 295, and 75 μg·mL−1, respectively, much lower than those attained for a commercial strobilurin fungicide (azoxystrobin). The extract was further tested ex situ against P. cinnamomi on artificially inoculated, excised stems of ‘Garnem’ almond rootstock, attaining complete protection at a dose of 782 μg·mL−1. The results suggest that holm oak bark extract may be a promising source of bioactive compounds against invasive forest pathogens, including the oomycete that is causing its decline, the so-called ‘seca’ in Spain.

Valorization of Quercus suber L. Bark as a Source of Phytochemicals with Antimicrobial Activity against Apple Tree Diseases

“…The obtained hydroxybenzoic acid profile was different from those previously reported [8,10], but exhibited similarities with that of Q. ilex bark [29], i.e., the presence of hydroxyciclopentenones, methylimidazoles, and hexadecanoic and nonanedioic acid/esters. Concerning other phytochemicals, the pyrazole 4-hydroxy-3-[[1,3-dihydroxy-2-propoxy]methyl]-1Hpyrazole-5-carboxamide is analogous to pirazofurin (a C-glycosyl compound that is 4-hydroxy-1H-pyrazole-5-carboxamide in which the hydrogen at position 3 has been replaced by a β-Dribofuranosyl group) with antineoplastic and antiviral properties [31].…”

Antibacterial Activity of Ginkgo biloba Extracts against Clavibacter michiganensis subsp. michiganensis, Pseudomonas spp., and Xanthomonas vesicatoria

“…The presence of catechol should be attributed to the rupture of catechin (a constituent identified by Lin et al [6] in the G. biloba leaves aqueous methanol extract) (Figure 2). Catechol had previously been identified in the extracts of Taxus baccata L. [31], Allium sativum L. [32], Sambucus nigra L. [33], and Quercus ilex L. [34], with concentrations ranging from 1.6 to 6.4% (compared to 3.3−7.9% in the extracts reported herein). Catechol oxidizes to melanoid pigments that are derivatives of benzoquinone, which is reported to have antimicrobial properties, slowing the decay of damaged fruits and other parts of plants.…”

Phytochemical Profiling of Sambucus nigra L. Flower and Leaf Extracts and Their Antimicrobial Potential against Almond Tree Pathogens

“…The efficacy of flower extract was tested by artificial inoculation of excised stems in controlled laboratory conditions. Inoculation was performed according to the procedure proposed by Matheron [ 72 ], with the modifications described by Sánchez-Hernández et al [ 73 ]. Briefly, young stems of healthy ‘Garnem’ ( P. amygdalus × P. persica ) rootstock plants with a 1.5 cm diameter were cut into 10 cm long sections using a grafting knife.…”