Growth inhibition of an Araucaria angustifolia (Coniferopsida) fungal seed pathogen, Neofusicoccum parvum, by soil streptomycetes

Fernando Rostirolla Dalmas,Elisabeth Magel,Hans-Peter Fiedler,Leandro Astarita,Luigi Defilippis,Robert Bauer,Rüdiger Hampp

doi:10.1186/1471-2180-13-168

Abstract

BackgroundAraucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. In this study we have isolated and characterized such a fungus and investigated the potential of Streptomyces Actinobacteria from the respective rhizosphere to act as antagonists.ResultsThe pathogenic fungus from Araucaria angustifolia seeds was identified by morphological markers (pore-associated Woronin-bodies) as belonging to the Pezizomycotina. Molecular data identified the fungus as Neofusicoccum parvum (Botryosphaeriaceae). Co-cultures on agar of this fungus with certain streptomycete isolates from the rhizosphere, and from the surface of Araucaria roots significantly reduced the growth of the fungus. HPLC analysis of the agar yielded streptomycete-specific exudate compounds which were partly identified. There were differences in compounds between single (bacteria, fungus) and dual cultures (bacteria + fungus).ConclusionStreptomycetes from the rhizosphere of Araucariaceae produce exudates which can suppress the development of pathogenic fungi in their seeds.

Highlights

Araucariaceae are important forest trees of the southern hemisphere
We present a list of exudate compounds produced by the fungus-inhibiting bacteria in single culture, and alterations due to the co-culture with the fungal pathogen
The pathogenic fungus on A. angustifolia seedlings: effects and identification After 50 days of germination, about 30% of Araucaria seedlings were infected by a fungus that promoted the death of the cotyledons and interrupted the connection between the seedling and the megagametophyte (Figure 1A, B)

Summary

Introduction

Araucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. Species of the coniferous genus Araucaria are important members of tropical and subtropical forests of the southern hemisphere [2]. Brazil pine (Araucaria angustifolia [Bertol.] Kuntze) was one of the most important species, economically and ecologically [3,4], occurring in mountain areas (above 800 m) of Southern Brazil, and dominated the forest vegetation [3]. Streptomycetes produce and release a wide variety of secondary metabolites. In studies with spruce seedlings, it could be shown that streptomycetes from the rhizosphere of a spruce stand could systemically improve resistance of seedlings against fungal infection [15]

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Conclusion