NGS_dehesa

Tree decline of holm oak in “dehesas” is a big threat to the sustainability of these ecosystems. Although Phytophthora cinnamomi is considered the main agent of holm oak decline, the relationships between different communities of biota influence tree decline and mortality. Little is known about the role of the fungal community in the decline syndrome of holm oak.• Soil samples of “dehesas” were collected and total DNA was extracted and analysed through metabarcoding techniques, to evaluate the specific composition and diversity of the fungal and oomycete communities and to study their relationship with the severity of the disease symptoms.• The fungal community included a wide range of pathogens and abundance of EcM key taxa. Phytophthora spp. dominated the oomycete community, but the species related to root rot did not appear among the most abundant, nor were they related directly to defoliation levels. A particular OTU belonging to the genus Trichoderma was strongly correlated with the scarcity of pathogenic Phytophthora spp.• The diversity and composition of both communities were key factors related to the severity of the decline symptoms. The differences in defoliation were related to changes in the functionality of soil microbiota and diversity levels of pathogenic species.