Abstract
Trichoderma are ubiquitous soil fungi that include species widely used as biocontrol agents in agriculture. Many isolates are known to secrete several secondary metabolites with different biological activities towards plants and other microbes. Harzianic acid (HA) is a T. harzianum metabolite able to promote plant growth and strongly bind iron. In this work, we isolated from the culture filtrate of a T. harzianum strain a new metabolite, named isoharzianic acid (iso-HA), a stereoisomer of HA. The structure and absolute configuration of this compound has been determined by spectroscopic methods, including UV-Vis, MS, 1D and 2D NMR analyses. In vitro applications of iso-HA inhibited the mycelium radial growth of Sclerotinia sclerotiorum and Rhizoctonia solani. Moreover, iso HA improved the germination of tomato seeds and induced disease resistance. HPLC-DAD experiments showed that the production of HA and iso HA was affected by the presence of plant tissue in the liquid medium. In particular, tomato tissue elicited the production of HA but negatively modulated the biosynthesis of its analogue iso-HA, suggesting that different forms of the same Trichoderma secondary metabolite have specific roles in the molecular mechanism regulating the Trichoderma plant interaction.
Highlights
The use of microbes for pest management in agriculture is one of the most effective biological control strategies
In this work we report the isolation and the characterization of a new metabolite named isoharzianic acid, a stereoisomer of harzianic acid, from the culture filtrate of a T. harzianum strain isolated from decomposing hardwood bark
The absolute configuration of 1, determined by X-ray diffraction studies, its antibiotic activity and plant growth promotion effect have been reported in a previous study [13]
Summary
The use of microbes for pest management in agriculture is one of the most effective biological control strategies. Secondary metabolites are chemically different natural compounds of relatively low molecular weight (in most cases < 3 kDa), that are mainly produced by microorganisms and plants, and typically associated to individual genera, species or strains. Some fungi of the genus Trichoderma may act as symbionts of plants, and are presently marketed as biopesticides and biofertilizers due to their ability to protect crops and promote vegetative growth [1,2,3]. These microbes are well known producers of secondary metabolites with different biological activities [8,9,10]. The influence of plant tissue on the production of HA and iso-HA has been examined
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