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

Holm oak ( subsp. (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 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 or its subspecies ( and ). 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%), -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 (responsible for pitch canker of spp.), (which causes chestnut blight), and (which causes 'root and crown rot' in a variety of hosts, including , conifers, , , etc.), obtaining EC values of 322, 295, and 75 μg·mL, respectively, much lower than those attained for a commercial strobilurin fungicide (azoxystrobin). The extract was further tested ex situ against on artificially inoculated, excised stems of 'Garnem' almond rootstock, attaining complete protection at a dose of 782 μg·mL. 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.