Gulypyrones A and B and Phomentrioloxins B and C Produced by Diaporthe gulyae, a Potential Mycoherbicide for Saffron Thistle (Carthamus lanatus)

Abstract

A virulent strain of Diaporthe gulyae, isolated from stem cankers of sunflower and known to be pathogenic to saffron thistle, has been shown to produce both known and previously undescribed metabolites when grown in either static liquid culture or a bioreactor. Together with phomentrioloxin, a phytotoxic geranylcyclohexenetriol recently isolated from a strain of Phomopsis sp., two new phytotoxic trisubstituted α-pyrones, named gulypyrones A and B (1 and 2), and two new 1,O- and 2,O-dehydro derivatives of phomentrioloxin, named phomentrioloxins B and C (3 and 4), were isolated from the liquid culture filtrates of D. gulyae. These four metabolites were characterized as 6-[(2S)2-hydroxy-1-methylpropyl]-4-methoxy-5-methylpyran-2-one (1), 6-[(1E)-3-hydroxy-1-methylpropenyl]-4-methoxy-3-methylpyran-2-one (2), 4,6-dihydroxy-5-methoxy-2-(7-methyl-3-methyleneoct-6-en-1-ynyl)cyclohex-2-enone (3), and 2,5-dihydroxy-6-methoxy-3-(7-methyl-3-methyleneoct-6-en-1-ynyl)cyclohex-3-enone (4) using spectroscopic and chemical methods. The absolute configuration of the hydroxylated secondary carbon of the 2-hydroxy-1-methylpropyl side chain at C-6 of gulypyrone A was determined as S by applying a modified Mosher's method. Other well-known metabolites were also isolated including 3-nitropropionic, succinic, and p-hydroxy- and p-methylbenzoic acids, p-hydroxybenzaldehyde, and nectriapyrone. When assayed using a 5 mM concentration on punctured leaf disks of weedy and crop plants, apart from 3-nitropropionic acid (the main metabolite responsible for the strong phytotoxicity of the culture filtrate), phomentrioloxin B caused small, but clear, necrotic spots on a number of plant species, whereas gulypyrone A caused leaf necrosis on Helianthus annuus plantlets. All other compounds were weakly active or inactive.

Fungal phytotoxins with potential herbicidal activity: chemical and biological characterization

“…94 Tested at different concentrations against the host plants of C. lanatus L. and some other weeds (M. annua L., C. album L., C. arvense L., Sonchus oleraceus L. and S. viridis L.), phomentrioloxin (75) caused the appearance of necrotic spots when applied to the leaves of both the host and non host plants at 6.85 mM. 95 Phomentrioloxins B (76) and C (77) showed the same unsaturated geranyl side chain of phomentrioloxin (75) but differed for the functionalities of the triolcyclohexene ring. Thus, it exhibited only phytotoxic properties and no toxicity to other nontarget organisms at the tested concentrations.…”

Selection, isolation, and identification of fungi for bioherbicide production

“…Diaporthe spp. are often described as producers of enzymes and secondary metabolites 27 with the potential as antibiotics, 28 fungicides, 29 and anticancer agents, 30 as well as that for preventing herbivory and for biological control of weeds 31, 32. Ethyl 2,4-dihydroxy-5,6-dimethylbenzoate, phomopsilactone, 33 phomopxanthone A and B, 34 taxol, 30 phomopsichalasin, 35 lactones, 29 nonenolides, phomonol, phomotone, 36 and phomophene are some of the compounds produced by members of the genus.…”

Bioherbicide production by Diaporthe sp. isolated from the Brazilian Pampa biome

“…For both targets, the efficiency of broths was 100%, since none seed germinated, independent of experimental run. Diaporthe is described as a producer of bioherbicide (Ash et al, 2010;Andolfi et al, 2015;Cimmino et al, 2013b). A virulent strain of Diaporthe gulyae, isolated from stem cankers of sunflower and known to be pathogenic to saffron thistle, has been shown to produce metabolites when grown in either static liquid culture or a bioreactor.…”

“…A virulent strain of Diaporthe gulyae, isolated from stem cankers of sunflower and known to be pathogenic to saffron thistle, has been shown to produce metabolites when grown in either static liquid culture or a bioreactor. Phomentrioloxin B caused small necrotic spots on a number of plant species, whereas gulypyrone A caused leaf necrosis on Helianthus annuus plantlets (Andolfi et al, 2015). Cimmino et al (2013b) tested several compounds produced in liquid culture by Phomopsis sp.…”