Anti-Phytophthora activity of root extracts from herbaceous species

The decline in Quercus suber (cork oak) and Q. rotundifolia (holm oak) “Montado” has been ascribed to the presence of the soil-borne pathogen Phytophthora cinnamomi. This oomycete has been considered a relevant agent related to the weakening and death of these oak species, both in Portugal and Spain (Extremadura and Andalucia). The control of this pathogen is rather difficult in the “Montado” ecosystem and the chemical control is not yet efficient. Integrated management strategies are needed to control the pathogen. The inhibitory effect of 15 aqueous root extracts from herbaceous species (Brassicaceae, Fabaceae, Lamiaceae and Poaceae) was tested in vitro on P. cinnamomi mycelial growth, sporangia and chlamydospore production and zoospore release and viability. The susceptibility of the selected herbaceous species to the pathogen was also evaluated in vivo (pot bioassay). Root extracts of some Brassicaceae species can suppress 80-100% P. cinnamomi activity in vitro showing no susceptibility to the pathogen in vivo conditions. The introduction in the “Montado” of a mix of non-hosts herbaceous species with allelopathic effect against the pathogen, incorporated in pastures might be a strategic measure to reduce its population, contributing also to improve soil suppressiveness and quality.