Plant roots release complex mixtures of bioactive molecules, including compounds that affect the activity and modify the composition of the rhizosphere microbiome. In this work, we investigated the initial phase of the interaction between tomato and an effective biocontrol strain of Trichoderma harzianum (T22). We found that root exudates (RE), obtained from plants grown in a split-root system and exposed to various biotic and abiotic stress factors (wounding, salt, pathogen attack), were able to stimulate the growth and act as chemoattractants of the biocontrol fungus. On the other hand, some of the treatments did not result in an enhanced chemotropism on Fusarium oxysporum f. sp. lycopersici, indicating a mechanism that may be selective for nonpathogenic microbes. The involvement of peroxidases and oxylipins, both known to be released by roots in response to stress, was demonstrated by using RE fractions containing these molecules or their commercial purified analogs, testing the effect of an inhibitor, and characterizing the complex pattern of these metabolites released by tomato roots both locally and systemically.

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Endophytic fungi have a great influence on plant health and growth, and are an important source of bioactive natural compounds. Organic extracts obtained from the culture filtrate of an endophytic strain of Talaromyces pinophilus isolated from strawberry tree (Arbutus unedo) were studied. Metabolomic analysis revealed the presence of three bioactive metabolites, the siderophore ferrirubin, the platelet-aggregation inhibitor herquline B and the antibiotic 3-O-methylfunicone. The latter was the major metabolite produced by this strain and displayed toxic effects against the pea aphid Acyrthosiphon pisum (Homoptera Aphidiidae). This toxicity represents an additional indication that the widespread endophytic occurrence of T. pinophilus may be related to a possible role in defensive mutualism. Moreover, the toxic activity on aphids could promote further study on 3-O-methylfunicone, or its derivatives, as an alternative to synthetic chemicals in agriculture.

Trichoderma fungi are effectively marketed worldwide as biocontrol agents and plant biostimulants on numerous crops due to their demonstrated effects in direct antagonism against fungal pathogens and plant growth promotion. Here, we examined the effects of single and combined applications of Trichoderma strains and their bioactive metabolites (BAMs) harzianic acid (HA), 6-pentyl-α-pyrone (6PP), and hydrophobin1 (HYTLO1) on the growth, yield, and nutrient uptake of soybean plants. Significant promotion of plant growth (up to 39%), as well as an increase in mineral content, was achieved with BAMs, used alone or combined with T. harzianum. Interestingly, the treatments also increased the level of fatty acids (oleic, linolenic, 11-eicosenoic, and stearic). This work demonstrates the usefulness of natural compound and microbe combinations to enhance oilseed productivity, and reports for the first time the ability of Trichoderma and/or its BAMs to increase the lipid content in harvested seeds.