Biocontrol Potential of Forest Tree Endophytes

Peer reviewe

Foliar endophytic fungi as potential protectors from pathogens in myrmecophytic Acacia plants

In defensive ant-plant interactions myrmecophytic plants express reduced chemical defense in their leaves to protect themselves from pathogens, and it seems that mutualistic partners are required to make up for this lack of defensive function. Previously, we reported that mutualistic ants confer plants of Acacia hindsii protection from pathogens, and that the protection is given by the ant-associated bacteria. Here, we examined whether foliar endophytic fungi may potentially act as a new partner, in addition to mutualistic ants and their bacteria inhabitants, involved in the protection from pathogens in myrmecophytic Acacia plants. Fungal endophytes were isolated from the asymptomatic leaves of A. hindsii plants for further molecular identification of 18S rRNA gene. Inhibitory effects of fungal endophytes were tested against Pseudomonas plant pathogens. Our findings support a potential role of fungal endophytes in pathogen the protection mechanisms against pathogens in myrmecophytic plants and provide the evidence of novel fungal endophytes capable of biosynthesizing bioactive metabolites

The role of pollination drops in animal pollination in the Mediterranean gymnosperm Ephedra fragilis (Gnetales)

The pollination drop (PD) is a sweet secretion produced by female cones of many gymnosperms whose main function is associated with the capture and transport of pollen to the nucellar surface of the ovule. Due to its high sugar content, PDs appear to be highly suitable for the attraction of animals that might act as potential pollinators for gymnosperms. In the present study, we evaluated the attraction of animals to female and male PDs (sugar-rich rewards) in plants of the Mediterranean shrub Ephedra fragilis in addition to their contribution to plant fitness. Animal exclusion experiments were conducted in Sa Dragonera Islet Natural Park (Western Mediterranean, Spain). In addition, a link between PD investment (PD concentration) and plant fitness was evaluated on plants of E. fragilis. Lizards and insects were the principal visitors to PDs offered by E. fragilis plants. Animals effectively contributed to plant fitness. Nevertheless, the fitness contribution was not as elevated as the contribution from wind pollination (~30 vs. 70 %, respectively). Increased plant investment on PDs significantly elevated fitness in plants of E. fragilis. The present study provides evidence that E. fragilis relies primarily on wind pollination, with pollination and fitness being supplemented by animal visitation. Additionally, besides its main role as pollen capture and germination, PDs act as a pollinator reward that benefits plant reproduction.We also thank MAE-AECID for the PhD grant to C.C.N.Peer reviewe

Molecular characterization of endophytic fungi associated with the roots of Chenopodium quinoa inhabiting the Atacama Desert, Chile

Plant roots can be highly colonized by fungal endophytes. This seems to be of particular importance for the survival of plants inhabiting stressful habitats. This study focused on the Identification of the fungal endophytic community associated with the roots of quinoa plants (Chenopodium quinoa) growing near the salt lakes of the Atacama Desert, Chile. One hundred endophytic fungi were isolated from healthy quinoa roots, and the internal transcribed spacer (ITS) region was sequenced for phylogenetic and taxonomic analysis. The isolates were classified into eleven genera and 21 distinct operational taxonomic units (OTUs). Despite a relatively high diversity of root endophytic fungi associated with quinoa plants, the fungal community was dominated by only the Ascomycota phyla. In addition, the most abundant genera were Penicillium, Phoma and Fusarium, which are common endophytes reported in plant roots. This study shows that roots of C. quinoa harbor a diverse group of endophytic fungi. Potential roles of these fungi in plant host tolerance to stressful conditions are discussed

Changes in Diversity and Community Composition of Root Endophytic Fungi Associated with Aristolochia chilensis along an Aridity Gradient in the Atacama Desert

Despite the widespread occurrence of fungal endophytes (FE) in plants inhabiting arid ecosystems, the environmental and soil factors that modulate changes in FE diversity and community composition along an aridity gradient have been little explored. We studied three locations along the coast of the Atacama Desert in Chile, in which the plant Aristolochia chilensis naturally grows, and that differ in their aridity gradient from hyper-arid to semi-arid. We evaluated if root-associated FE diversity (frequency, richness and diversity indexes) and community composition vary as a function of aridity. Additionally, we assessed whether edaphic factors co-varying with aridity (soil water potential, soil moisture, pH and nutrients) may structure FE communities. We expected that FE diversity would gradually increase towards the aridity gradient declines, and that those locations that had the most contrasting environments would show more dissimilar FE communities. We found that richness indexes were inversely related to aridity, although this pattern was only partially observed for FE frequency and diversity. FE community composition was dissimilar among contrasting locations, and soil water availability significantly influenced FE community composition across the gradient. The results indicate that FE diversity and community composition associated with A. chilensis relate to differences in the aridity level across the gradient. Overall, our findings reveal the importance of climate-related factors in shaping changes in diversity, structure and distribution of FE in desert ecosystems

Glucanases and Chitinases as Causal Agents in the Protection of Acacia Extrafloral Nectar from Infestation by Phytopathogens1[W][OA]

Nectars are rich in primary metabolites and attract mutualistic animals, which serve as pollinators or as an indirect defense against herbivores. Their chemical composition makes nectars prone to microbial infestation. As protective strategy, floral nectar of ornamental tobacco (Nicotiana langsdorffii × Nicotiana sanderae) contains “nectarins,” proteins producing reactive oxygen species such as hydrogen peroxide. By contrast, pathogenesis-related (PR) proteins were detected in Acacia extrafloral nectar (EFN), which is secreted in the context of defensive ant-plant mutualisms. We investigated whether these PR proteins protect EFN from phytopathogens. Five sympatric species (Acacia cornigera, A. hindsii, A. collinsii, A. farnesiana, and Prosopis juliflora) were compared that differ in their ant-plant mutualism. EFN of myrmecophytes, which are obligate ant-plants that secrete EFN constitutively to nourish specialized ant inhabitants, significantly inhibited the growth of four out of six tested phytopathogenic microorganisms. By contrast, EFN of nonmyrmecophytes, which is secreted only transiently in response to herbivory, did not exhibit a detectable inhibitory activity. Combining two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis with nanoflow liquid chromatography-tandem mass spectrometry analysis confirmed that PR proteins represented over 90% of all proteins in myrmecophyte EFN. The inhibition of microbial growth was exerted by the protein fraction, but not the small metabolites of this EFN, and disappeared when nectar was heated. In-gel assays demonstrated the activity of acidic and basic chitinases in all EFNs, whereas glucanases were detected only in EFN of myrmecophytes. Our results demonstrate that PR proteins causally underlie the protection of Acacia EFN from microorganisms and that acidic and basic glucanases likely represent the most important prerequisite in this defensive function