Phytotoxic Metabolites Isolated from Neufusicoccum batangarum, the Causal Agent of the Scabby Canker of Cactus Pear (Opuntia ficus-indica L.)

Identification of Lasiodiplodia species inciting stem rot of dragon fruit in India through polyphasic approach

Lasiodiplodia species commonly thrive as endophytes, saprobes, and plant pathogens in tropical and subtropical regions. Association of Lasiodiplodia species causing stem rot in dragon fruit in the coastal belt of Odisha, eastern India, has been illustrated here. The stem rot disease was characterized by yellowing of the stem, followed by softening of the stem tissues with fungal fructifications of the pathogen in the affected tissues. On the basis of macro- and micromorphological characteristics, the four fungal isolates recovered from diseased stems were identified initially as Lasiodiplodia species. By comparing DNA sequences within the NCBI GenBank database as well as performing a multigene phylogenetic analysis involving the internal transcribed spacer region (ITS-rDNA), β-tubulin (β-tub), and elongation factor-alpha (EF1-α) genes, the identity of Lasiodiplodia isolates was determined. The isolate CHES-21-DFCA was identified as Lasiodiplodia iraniensis (syn: L. iranensis) and the remaining three isolates, namely CHES-22-DFCA-1, CHES-22-DFCA-2, and CHES-22-DFCA-3, as L. theobromae. Although pathogenicity studies confirmed both L. iraniensis and L. theobromae were responsible for stem rot in dragon fruit, L. iraniensis was more virulent than L. theobromae. This study established the association of Lasiodiplodia species with stem rot in dragon fruit using a polyphasic approach. Further investigations are required, particularly related to on host-pathogen-weather interaction and spatiotemporal distribution across the major dragon fruit-growing areas of the country to formulate prospective disease management strategies. This is the first report on these two species of Lasiodiplodia inflicting stem rot in Hylocereus species in India.

Diversity of Mycotoxins and Other Secondary Metabolites Recovered from Blood Oranges Infected by Colletotrichum, Alternaria, and Penicillium Species

This study identified secondary metabolites produced by Alternaria alternata, Colletotrichum gloeosporioides, and Penicillium digitatum in fruits of two blood orange cultivars before harvest. Analysis was performed by UHPLC-Q-TOF-MS. Three types of fruits were selected, asymptomatic, symptomatic showing necrotic lesions caused by hail, and mummified. Extracts from peel and juice were analyzed separately. Penicillium digitatum was the prevalent species recovered from mummified and hail-injured fruits. Among 47 secondary metabolites identified, 16, 18, and 13 were of A. alternata, C. gloeosporioides, and P. digitatum, respectively. Consistently with isolations, indicating the presence of these fungi also in asymptomatic fruits, the metabolic profiles of the peel of hail-injured and asymptomatic fruits did not differ substantially. Major differences were found in the profiles of juice from hail-injured and mummified fruits, such as a significant higher presence of 5,4-dihydroxy-3,7,8-trimethoxy-6C-methylflavone and Atrovenetin, particularly in the juice of mummified fruits of the Tarocco Lempso cultivar. Moreover, the mycotoxins patulin and Rubratoxin B were detected exclusively in mummified fruits. Patulin was detected in both the juice and peel, with a higher relative abundance in the juice, while Rubratoxin B was detected only in the juice. These findings provide basic information for evaluating and preventing the risk of contamination by mycotoxins in the citrus fresh fruit supply chain and juice industry.

Novel terpestacin derivatives with l-amino acid residue as anticancer agents against U87MG-derived glioblastoma stem cells

Based on the natural product terpestacin, seventeen derivatives (1-17) with various l-amino acid side chains were designed and synthesized. Their anticancer activities against U87MG-derived glioblastoma stem cells (GSCs) were evaluated, and compounds 5, 11, 13 and 15 showed strong abilities to inhibit the proliferation (IC₅₀ = 2.8-6.9 μM) and tumorsphere formation of GSCs. Besides, compounds 13 and 15 could effectively induce apoptosis and significantly inhibit the invasion of GSCs (95 and 97 % inhibition, respectively, at 2.5 μM). The levels of CD133 marker in GSCs also decreased in dose-dependent manners after the treatment of these active compounds. Compared to terpestacin and the positive control A1938, our derivatives showed stronger activities and compounds 13 and 15 are promising candidates for further development as anticancer agents by targeting GSCs.

Isolation and Identification of Secondary Metabolites Produced by Phytopathogenic Fungus Corynespora cassiicola from Hevea brasiliensis

The secondary metabolites of the phytopathogenic fungus Corynespora cassiicola CC01 from Hevea brasiliensis were investigated. As a result, two new compounds, 5-acetyl-7-hydroxy-6- methoxybenzofuran-2(3H)-one (1) and (S)-2-(2,3-dihydrofuro [3,2-c]pyridin-2-yl)propan-2-ol (2), together with seven known compounds, 4,6,8-trihydroxy-3,4-dihydronaphthalen-1(2H)-one (3), 3,6,8-trihydroxy-3,4-dihydronaphthalen-1(2H)-one (4), curvulin acid (5), 2-methyl-5-carboxymethyl- 7-hydroxychromone (6), tyrosol (7), p-hydroxybenzoic acid (8) and cerevisterol (9), were isolated from the fermentation extract by comprehensive silica gel, reverse phase silica gel, Sephadex-LH20 column chromatography and high-performance liquid chromatography (HPLC). The structures of these compounds were identified by using high-resolution electrospray mass spectrometry (HRESIMS), nuclear magnetic resonance spectroscopy (NMR), optical rotation, ultraviolet and infrared spectroscopy techniques and a comparison of NMR data with those reported in the literature. Compounds 1 and 2 were new compounds, and compounds 3–9 were discovered from this phytopathogenic fungus for the first time. Compounds 1–9 were tested for phytotoxicity against the fresh tender leaf of Hevea brasiliensis, and the results show that none of them were phytotoxic. Additionally, these compounds were subjected to an antimicrobial assay against three bacteria (E. coli, methicillin-resistant Staphylococcus aureus and Micrococcus luteus), but they showed no activity.

Antibiotic and Nematocidal Metabolites from Two Lichen Species Collected on the Island of Lampedusa (Sicily)

The antibiotic and nematocidal activities of extracts from two coastal lichen species collected on Lampedusa Island (Sicily), Ramalina implexa Nyl. and Roccella phycopsis Ach., were tested. Methyl orsellinate, orcinol, (+)-montagnetol, and for the first time 4-chlororcinol were isolated from Roccella phycopsis. (+)-Usnic acid was obtained from Ramalina implexa. The crude organic extract of both lichen species showed strong antibiotic activity against some bacterial species and nematocidal activity. Among all the pure metabolites tested against the infective juveniles (J2) of the root-knot nematode (RKN) Meloydogine incognita, (+)-usnic acid, orcinol, and (+)-montagnetol had significant nematocidal activity, comparable with that of the commercial nematocide Velum^® Prime, and thus they showed potential application in agriculture as a biopesticide. On the contrary, methyl orsellinate and 4-chlororcinol had no nematocidal effect. These results suggest that the substituent pattern at ortho-para-position in respect to both hydroxyl groups of resorcine moiety, which is present in all metabolites, seems very important for nematocidal activity. The organic extracts of both lichens were also tested against some Gram-positive and Gram-negative bacteria. Both extracts were active against Gram-positive species. The extract of Ramalina implexa showed, among Gram-negative species, activity against Escherichia coli and Acinetobacter baumannii, while that from Roccella phycopsis was effective towards all test strains, with the exception of Pseudomonas aeruginosa. The antimicrobial activity of (+)-usnic acid, methyl orsellinate, and (+)-montagnetol is already known, so tests were focused on orcinol and 4-chlororcinol. The former showed antibacterial activity against all Gram positive and Gram-negative test strains, with the exception of A. baumannii and K. pneumoniae, while the latter exhibited a potent antibacterial activity against Gram-positive test strains and among Gram-negative strains, was effective against A. baumannii and K. pneumonia. These results suggest, for orcinol and 4-chlororcinol, an interesting antibiotic potential against both Gram-positive and Gram-negative bacterial strains.

Fusarium and Neocosmospora Species Associated with Rot of Cactaceae and Other Succulent Plants

Infections by Fusarium and Fusarium-like species on cacti and other succulent plants cause the syndrome known as Fusarium dry rot and soft rot. There are only few records of Fusarium species as pathogens of cacti and other succulent plants from Iran. The objective of this study was the identification and characterization of fusarioid species recovered from ornamental succulents in Shiraz County, Iran. Three fusarioid species, including F. oxysporum, F. proliferatum, and Neocosmospora falciformis (formerly F. falciforme), were recovered from 29 diverse species of cacti and other succulents with symptoms of Fusarium dry rot and soft rot. The three fungal species were identified on the basis of morphological characters and the phylogenetic analysis of the translation elongation factor1-α (tef1) nuclear gene. The F. oxysporum isolates were identified as F. oxysporum f. sp. opuntiarum. The pathogenicity of the three fusarioid species was tested on a range of economically important ornamental succulents, mostly in the Cactaceae family. The three species showed a broad host spectrum and induced different types of symptoms on inoculated plants, including soft and dry rot, chlorosis, necrotic spots, wilt, drying, root and crown rot. This is the first report of N. falciformis as a pathogen of succulent plants worldwide.

Polysaccharide Based Polymers Produced by Scabby Cankered Cactus Pear (Opuntia ficus-indica L.) Infected by Neofusicoccum batangarum: Composition, Structure, and Chemico-Physical Properties

Neofusiccocum batangarum is the causal agent of scabby canker of cactus pear (Opuntia ficus-indica L.). The symptoms of this disease are characterized by crusty, perennial cankers, with a leathery, brown halo. Characteristically, a viscous polysaccharide exudate, caking on contact with air, leaks from cankers and forms strips or cerebriform masses on the surface of cactus pear cladodes. When this polysaccharide mass was partial purified, surprisingly, generated a gel. The TLC analysis and the HPLC profile of methyl 2-(polyhydroxyalkyl)-3-(o-tolylthiocarbomoyl)-thiazolidine-4R-carboxylates obtained from the mixture of monosaccharides produced by acid hydrolysis of the three EPSs examined in this research work [the polysaccharide component of the exudate (EPSC) and the EPSs extracted from asymptomatic (EPSH) and symptomatic (EPSD) cladodes] showed the presence of d-galactose, l-rhamnose, and d-glucose in a 1:1:0.5 ratio in EPSC while d-galactose, l-rhamnose, d-glucose, and d-xylose at the same ratio were observed in EPSH and EPSD. The presence of uronic acid residues in EPSC was also showed by solid state NMR and IR investigation. Furthermore, this manuscript reports the chemical-physical characterization of the gel produced by the infected cactus pear.

Identification and Functional Characterization of the Gene Cluster Responsible for Fusaproliferin Biosynthesis in Fusarium proliferatum

The emerging mycotoxin fusaproliferin is produced by Fusarium proliferatum and other related Fusarium species. Several fungi from other taxonomic groups were also reported to produce fusaproliferin or the deacetylated derivative, known as siccanol or terpestacin. Here, we describe the identification and functional characterization of the Fusarium proliferatum genes encoding the fusaproliferin biosynthetic enzymes: a terpenoid synthase, two cytochrome P450s, a FAD-oxidase and an acetyltransferase. With the exception of one gene encoding a CYP450 (FUP2, FPRN_05484), knock-out mutants of the candidate genes could be generated, and the production of fusaproliferin and intermediates was tested by LC-MS/MS. Inactivation of the FUP1 (FPRN_05485) terpenoid synthase gene led to complete loss of fusaproliferin production. Disruption of a putative FAD-oxidase (FUP4, FPRN_05486) did not only affect oxidation of preterpestacin III to terpestacin, but also of new side products (11-oxo-preterpstacin and terpestacin aldehyde). In the knock-out strains lacking the predicted acetyltransferase (FUP5, FPRN_05487) fusaproliferin was no longer formed, but terpestacin was found at elevated levels. A model for the biosynthesis of fusaproliferin and of novel derivatives found in mutants is presented.

Inhibition of Mycotoxigenic Fungi in Different Vegetable Matrices by Extracts of Trichoderma Species

Post-harvest fungal diseases of plant products are a serious concern leading to economic losses and health risks. Moreover, the use of synthetic chemical fungicides to prevent these diseases is limited due to toxic residues. This study aimed at determining the effective dose of extracts of Trichoderma asperellum IMI393899 (TE1) and Trichoderma atroviride TS (TE2) in inhibiting the contamination by mycotoxigenic fungi on different plant matrices. Extracts were tested on tomatoes contaminated by Fusarium verticillioides and Fusarium graminearum, wheat contaminated by Penicillium verrucosum and maize contaminated by Aspergillus flavus. The efficacy of extracts was evaluated at two time intervals after treatment, 4 and 11 days for tomato, and 10 and 20 days for both wheat and maize. Both extracts showed a significant inhibitory activity on mycotoxigenic pathogens and significantly reduced Log CFU/g compared to the control. Moreover, the extracts reduced mycotoxin production in a dose dependent manner and with a long-lasting effect. The ochratoxin A was reduced by both extracts but only the extract TE2 was effective in reducing aflatoxins, whereas TE1 treatment increased their synthesis.

Cytotoxicity and Nitric Oxide Production Inhibitory Activities of Compounds Isolated from the Plant Pathogenic Fungus Curvularia sp

Chemical investigation of the mycelia of the pathogenic fungus Curvularia sp. which was isolated from a leaf of Dactyloctenium aegyptium (crowfoot grass), resulted in the isolation of a new compound, curvulariahawadride (5), along with five known compounds (1-4, and 6). Their structures were determined on the basis of spectroscopic data, including 1D and 2D NMR and HRESIMS. The absolute configuration of 5 was established from experimental and calculated electronic circular dichroism (ECD). Compounds 1, 3, and 5 showed nitric oxide (NO) production inhibitory activity with IC₅₀ values of 53.7, 32.8, and 12.8 µM, respectively. Compounds 2 and 4 showed significant cytotoxicity against lung cancer A549, colorectal cancer SW480, and leukemic K562 cells with an IC₅₀ ranging value of 11.73 to 17.59 µM.

Bot Gummosis of Lemon (Citrus × limon) Caused by Neofusicoccum parvum

Neofusicoccum parvum, in the family Botryosphaeriaceae, was identified as the causal agent of bot gummosis of lemon (Citrus × limon) trees, in the two major lemon-producing regions in Italy. Gummy cankers on trunk and scaffold branches of mature trees were the most typical disease symptoms. Neofusicoccum parvum was the sole fungus constantly and consistently isolated from the canker bark of symptomatic lemon trees. It was identified on the basis of morphological characters and the phylogenetic analysis of three loci, i.e., the internal transcribed spacer of nuclear ribosomal DNA (ITS) as well as the translation elongation factor 1-alpha (TEF1) and β-tubulin (TUB2) genes. The pathogenicity of N. parvum was demonstrated by wound inoculating two lemon cultivars, 'Femminello 2kr' and 'Monachello', as well as citrange (C. sinensis × Poncirus trifoliata) 'Carrizo' rootstock. In artificial inoculations, the fungus was very aggressive on lemons and weakly virulent on citrange, consistently with symptoms observed in the field as a consequence of natural infections. This is the first report of N. parvum, both in a wide and in a strict taxonomic sense, as a pathogen of lemon in Italy.

Phytotoxic Secondary Metabolites from Fungi

Fungal phytotoxic secondary metabolites are poisonous substances to plants produced by fungi through naturally occurring biochemical reactions. These metabolites exhibit a high level of diversity in their properties, such as structures, phytotoxic activities, and modes of toxicity. They are mainly isolated from phytopathogenic fungal species in the genera of Alternaria, Botrytis, Colletotrichum, Fusarium, Helminthosporium, and Phoma. Phytotoxins are either host specific or non-host specific phytotoxins. Up to now, at least 545 fungal phytotoxic secondary metabolites, including 207 polyketides, 46 phenols and phenolic acids, 135 terpenoids, 146 nitrogen-containing metabolites, and 11 others, have been reported. Among them, aromatic polyketides and sesquiterpenoids are the main phytotoxic compounds. This review summarizes their chemical structures, sources, and phytotoxic activities. We also discuss their phytotoxic mechanisms and structure-activity relationships to lay the foundation for the future development and application of these promising metabolites as herbicides.

Production and identification of two antifungal terpenoids from the Posidonia oceanica epiphytic Ascomycota Mariannaea humicola IG100

Background

Marine fungi are an important repository of bioactive molecules with great potential in different technological fields, the annual number of new compounds isolated from marine fungi is impressive and the general trend indicates that it is still on the rise. In this context, the antifungal and antimicrobial activity of the marine strain Mariannaea humicola IG100 was evaluated and two active terpenoids were isolated and characterized.

Methods

Preliminary screening of activity of marine strain IG100 was carried out by agar plug diffusion methods against fungal (Penicillium griseofulvum TSF04) and bacterial (Bacillus pumilus KB66 and Escherichia coli JM109) strains. Subsequently, inhibition tests were done by using the cultural broth and the organic extract (ethyl acetate, EtOAc) by the agar well diffusion methods. The main active fractions were identified and tested for their antifungal activity against P. griseofulvum TSF04 in a 24 wells microplate at different concentrations (1000, 100, 10 and 1.0 µg/mL). Two active compounds were characterized and their relative MIC measured by the broth micro-dilution methods in a 96-well microplate against Aspergillus flavus IG133, P. griseofulvum TSF04, and Trichoderma pleuroticola IG137.

Results

Marine strain IG100 presented significant antifungal activity associated with two active compounds, the terpenoids terperstacin 1 and 19-acetyl-4-hydroxydictyodiol 2. Their MIC values were measured for A. flavus (MIC of 7.9 µg/mL and 31.3 µg/mL for 1 and 2, respectively), P. griseofulvum (MIC of 25 µg/mL and 100 µg/mL for 1 and 2, respectively) and T. pleuroticola (MIC > 500 µg/mL and 125 µg/mL for 1 and 2, respectively). They showed a rather good fungistatic effect.

Conclusions

In this study, the first marine strain of M. humicola (IG100) was investigated for the production of bioactive molecules. Strain IG100 produced significant amounts of two bioactive terpenoids, terperstacin 1 and 19-acetyl-4-hydroxydictyodiol 2. The two compounds showed significant antifungal activities against A. flavus IG133, T. pleuroticola IG137 and P. griseofulvum TSF04. Compound 2 was identified for the first time in fungi.