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No full textThe effect of stereochemistry on the biological activity of natural phytotoxins, fungicides, insecticides and herbicides
No full textPhytotoxins are secondary microbial metabolites that play an essential role in the development of disease symptoms induced by fungi on host plants. Although phytotoxins can cause extensive—and in some cases devastating—damage to agricultural crops, they can also represent an important tool to develop natural herbicides when produced by fungi and plants to inhibit the growth and spread of weeds. An alternative strategy to biologically control
parasitic plants is based on the use of plant and fungal metabolites, which stimulate seed germination in the absence of the host plant. Nontoxigenic fungi also produce bioactive metabolites with potential fungicide and insecticide activity, and could be applied for crop protection. All these metabolites represent important tools to develop eco-friendly pesticides. This review deals with the relationships between the biological activity of some phytotoxins, seed germination stimulants, fungicides and insecticides, and their stereochemistr
Phytotoxic Terpenes Produced by Phytopathogenic Fungi and Allelopathic Plants
No full textThis review is about the isolation as well as chemical and biological characterization of simple and complex mono-, sesqui-, di-, sester- and tri-terpenes produced by fungal pathogens of agrarian and forest plants and by some allelopathic plants. In several cases, the structure activity relationships are also discussed, as well as their potential application in agriculture as natural safe herbicides, fungicides and bactericides. Furthermore, the potential application of some fungal terpenes as anticancer compounds with a new mode of action is also discussed
Analytic Methods of Bioactive Metabolites Produced by plants and Microorganisms
No full textA review. HPLC and/or HPTLC, mass spectrometric and immunochem. methods for the anal. of natural bioactive metabolites are described. In particular, methods developed for the anal. of metabolites from plants and microorganisms in complex mixts. represent an important tool to investigate the biosynthesis and the mode of action of these metabolites for their large scale prodn. and for their practical applications
Fungal phytotoxins for control of Cirsium arvense and Sonchus arvensis
No full textPerennial weeds, including Cirsium arvense and Sonchus arvensis, are a common problem in crop fields, especially in agricultural systems with reduced herbicide usage. Herbicides recommended for control of these perennials generally are restricted to only a few active ingredients that tend to have low selectivity, especially on dicot crops. Microbial phytotoxins or their synthetic analogues may be candidates for new weed-control options. Many plant pathogens, especially necrotrophic or hemibiotrophic fungi, produce a range of phytotoxins responsible for disease damage and may be a source of such useful metabolites. Several pathogens, including Stagonospora cirsii and Ascochyta sonchi, were found commonly on C. arvense and S. arvensis, and these fungi also produce phytotoxic metabolites. Phyllosticta cirsii and Phomopsis cirsii, belonging to two well-known toxin-producing genera, have also been proposed for biocontrol of C. arvense. Phytotoxins isolated from these fungal pathogens are metabolites belonging to several classes of natural compounds including enol pyruvic acid derivatives, cytochalasins, nonenolides, oxazatricycloalkenones, pentasubstituted bicyclooctatrienyl ester of acetic acid, pentasubstituted hexahydrobenzodioxine carboxylic acid methyl ester, and β-nitropropionic acid. Some of these metabolites may be used as biomarkers, for studies on mode of action and development of structure-activity relationships
Phytotoxic nonenolides produced by fungi pathogenic for crops and weeds
No full textPinolidoxin, 2-hexadionoyloxy-7-hydroxy-9-propyl-5-nonen-9-olide, is the first phytotoxic nonenolide, isolated from some of us on 1993, together three minor ones as the main toxin produced by Ascochyta pinodes.1 This is the fungal causal agent of pea anthracnose.
Successively, phytotoxic nonenolide as putaminoxin, the main one, the close related putaminoxins B-D were also isolated from Phoma putaminum, the fungus proposed as mycoherbicide to biological control Erigeron annuus, a widespread weed in the pasture of northern emisphere.2 Later, stagonolide, a new nonenolide, was also isolated as the main toxin from liquid culture of Stagonospora cirsii proposed for the biological control of Cirsium arvense and Sonchus arvensis, two very noxious perennial weeds of several agrarian crops, essentially cereals. Successively nine related new nonenolides were isolated together to the well known modiolide A, from solid cultures of the same fungus.3 So that some studies were carried out using the toxins some their natural analogues and hemisynthetic derivatives to carry out studies on the structure-activity relationships and on their mode of action.4
Recently, from a strain of Ascochyta pinodes isolated in Spain from infected pea and grown in liquid culture were isolated herbarumin II, and 2-epi-herbarumin II together with a new nonenolide, named pinolide. In this communication an overview on the phytotoxic fungal nonenolides will be illustrated as well as the chemical and biological characterization of pinolide and the potential practical application of some of them as natural eco-friendly herbicides
Pyrenophoric Acid, a Phytotoxic Sesquiterpenoid Penta-2,4-dienoic Acid Produced by a Potential Mycoherbicide,Pyrenophora semeniperda
No full textA new phytotoxic sesquiterpenoid penta-2,4-dienoic acid, named pyrenophoric acid, was isolated from solid wheat seed culture of Pyrenophora semeniperda, a fungal pathogen proposed as a mycoherbicide for biocontrol of cheatgrass (Bromus tectorum) and other annual bromes. These bromes are serious weeds in winter cereals and also on temperate semiarid rangelands. Pyrenophoric acid was characterized as (2Z,4E)-5-[(7S,9S,10R,12R)-3,4-dihydroxy-2,2,6-trimethylcyclohexyl)]-3-methylpenta-2,4-dienoic acid by spectroscopic and chemical methods. The relative stereochemistry of pyrenophoric acid was assigned using 1H,1H couplings and NOESY experiments, while its absolute configuration
was determined by applying the advanced Mosher’s method. Pyrenophoric acid is structurally quite closely related to the plant growth regulator abscisic acid. When bioassayed in a cheatgrass coleoptile elongation test at 10−3 M, pyrenophoric acid showed strong phytotoxicity, reducing coleoptile elongation by 51% relative to the control. In a mixture at 10−4 M, its negative effect on coleoptile elongation was additive with that of cytochalasin B, another phytotoxic compound found in the wheat seed culture extract of this fungus, demonstrating that the extract toxicity observed in earlier studies was due to the combined action of multiple phytotoxic compounds
Natural metabolites for parasitic weed management
No full textCompounds of natural origin, such as phytotoxins produced by fungi or natural amino acids, could be used in parasitic weed management strategies by interfering with the early growth stages of the parasites. These metabolites could inhibit seed germination or germ tube elongation, so preventing attachment to the host plant, or, conversely, stimulate seed germination in the absence of the host, contributing to a reduction in the parasite seed bank. Some of the fungal metabolites assayed were very active even at very low concentrations, such as some macrocyclic trichothecenes,which at 0.1 ??M strongly suppressed the germination of Orobanche ramosa L. seeds. Interesting resultswere also obtainedwith somenovel toxins, such as phyllostictine A, highly active in reducing germ tube elongation and seed germination both of O. ramosa and of Cuscuta campestris Yuncker. Among the amino acids tested, methionine and arginine were particularly interesting, as they were able to suppress seed germination at concentrations lower than 1mM. Some of the fungal metabolites tested were also able to stimulate the germination of O. ramosa seed
Chlorosphaeropsidone and epichlorosphaeropsidone, two new chlorinated dimedone methyl ethers isolated from liquid cultures of Sphaeropsis sapinea f. sp. cupressi
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