Abstract
Phytophthora root rot caused by the pathogen Phytophthora cinnamomi is one of the main causes of oak mortality in Mediterranean open woodlands, the so-called dehesas. Disease control is challenging; therefore, new alternative measures are needed. This study focused on searching for natural biocontrol agents with the aim of developing integrated pest management (IPM) strategies in dehesas as a part of adaptive forest management (AFM) strategies. Native Trichoderma spp. were selectively isolated from healthy trees growing in damaged areas by P. cinnamomi root rot, using Rose Bengal selective medium. All Trichoderma (n = 95) isolates were evaluated against P. cinnamomi by mycelial growth inhibition (MGI). Forty-three isolates presented an MGI higher than 60%. Twenty-one isolates belonging to the highest categories of MGI were molecularly identified as T. gamsii, T. viridarium, T. hamatum, T. olivascens, T. virens, T. paraviridescens, T. linzhiense, T. hirsutum, T. samuelsii, and T. harzianum. Amongst the identified strains, 10 outstanding Trichoderma isolates were tested for mycoparasitism, showing values on a scale ranging from 3 to 4. As far as we know, this is the first report referring to the antagonistic activity of native Trichoderma spp. over P. cinnamomi strains cohabiting in the same infected dehesas. The analysis of the tree health status and MGI suggest that the presence of Trichoderma spp. might diminish or even avoid the development of P. cinnamomi, protecting trees from the worst effects of P. cinnamomi root rot.
Highlights
Soil microbes are key elements regulating ecological functions in natural ecosystems
To carry out the present work, some of the previously evaluated trees were selected according to the following characteristics: (i) trees growing in a plot with positive isolation of Phytophthora cinnamomi according to the data of the SEDA Network and to Ruiz-Gómez et al [33]; (ii) mean holm oak defoliation of plots increasing after 4 years; and (iii) trees with positive detection of Trichoderma sp
The information obtained from the reviewed literature, this is the first work characterizing the antagonistic activity between native Trichoderma spp. and P. cinnamomi strains, isolated from holm oak trees presenting symptoms of tolerance/resistance to the disease caused by this aggressive pathogen in infected dehesas
Summary
Soil microbes are key elements regulating ecological functions in natural ecosystems. The specific composition of the microbial community and its biodiversity are directly related to the phytosanitary status of the plant community [2,3], influenced by the presence of soil pathogens and by beneficial species such as ectomycorrhizae (EcM), arbuscular mycorrhizae (AM), or nitrogen-fixing bacteria. This beneficial community plays a variety of roles, including enhancement of water and nutrient uptake of roots, plant pest or plant pathogen control, and improvement in soil fertility and nutrient availability [4,5]. It is one of the most threatened oak species by the root rot caused by soil-borne oomycetes [12]
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