Antifungal activity of liquid waste obtained from the detoxification of steam-exploded plant biomass against plant pathogenic fungi

The antifungal activity of steam-exploded liquid waste (SELW) produced by the detoxification of steam-exploded biomass of Miscanthus sinensis, Arundo donax and wheat straw for 2nd generation industrial bioethanol production was studied against plant pathogenic fungi for the first time. Quantification of fermentation inhibitors (2-furaldehyde, 5-hydroxymethylfurfural, acetic and formic acid) was carried out by standard methods. Mycelial growth inhibition and conidial germination of eight fungal strains [Alternaria alternata, Botrytis cinerea, Colletotrichum acutatum, Cladosporium fulvum, Fusarium oxysporum f. sp. lycopersici (FOL), F. oxysporum f. sp. melonis (FOM), F. solani f. sp. pisi and Verticillium dahliae] were evaluated in vitro at different dilution rates (1:2, 1:4 and 1:8) for each SELW. Disease suppressiveness was assessed in vivo in eight horticultural pathosystems (A. alternata/tomato, B. cinerea/tomato, C. acutatum/strawberry, C. fulvum/tomato, FOL/tomato, FOM/melon, F. solani f. sp. pisi/pea and V. dahliae/eggplant) under greenhouse conditions. Pathogen suppression by each SELW, applied both in spray form on to tomato leaves and skins of tomato and strawberry, and by means of dipping method in watering suspensions on to seedling root systems of tomato, melon, pea and eggplant, was evaluated at dilution rates of 1:2, 1:4 and 1:8 using irrigation water during curative and preventive treatments. Investigations carried out in vitro showed that M. sinensis SELW was more suppressive than wheat straw SELW, and A. donax SELW was less suppressive than wheat straw SELW at the lowest dilution rates. Relationships between the concentration of 2-furaldehyde, acetic and formic acid present in SELWs and their antifungal effect were found. Moreover, B. cinerea, C. fulvum, V. dahliae, A. alternata, C. acutatum and F. solani f. sp. pisi were more effectively inhibited than FOL and FOM. Investigations performed in vivo showed that SELWs of M. sinensis and wheat straw can be diluted at a 1:2 rate and used for controlling six fungal diseases during preventive treatments. In particular, they can be used by dipping of the root systems during transplanting in the case of F. solani f. sp. pisi/pea and V. dahliae/eggplant; on the other hand, they can be nebulized on to the leaves and fruits before symptoms appearance in the case of A. alternata/tomato, B. cinerea/tomato, C. acutatum/strawberry and C. fulvum/tomato. This study is of particular interest because it points out how these SELWs could be employed in horticultural crop protection in Southern Italy, thereby making it possible to effectively combine industrial production of 2nd generation biofuels with sustainable horticulture under greenhouse conditions.     

Antifungal activity of polyacetylenes isolated from Cirsium japonicum roots against various phytopathogenic fungi

Antifungal substances from a methanol extract of Cirsium japonicum roots were purified and characterized, and their antifungal activities against various plant pathogens were evaluated. Three polyacetylene substances were isolated from roots of C. japonicum using repeated column chromatography; these were identified as ciryneol A, ciryneol C and 1-heptadecene-11,13-diyne-8,9,10-triol by mass and nuclear magnetic resonance spectral analyses. In vitro antifungal activity of the three substances varied according to compound and target species. Magnaporthe oryzae, Colletotrichum coccodes, Colletotrichum acutatum, Pythium ultimum and Botrytis cinerea were relatively sensitive to the three polyacetylenes, with IC₅₀ values below 50 μg mL⁻¹. In vivo, they all showed similar and broad antifungal spectra against the seven plant diseases tested. At 500 μg mL⁻¹, all three compounds effectively suppressed the development of rice blast, rice sheath blight, tomato late blight, wheat leaf rust and red pepper anthracnose, with control values over 90%. They were highly active especially against wheat leaf rust; they controlled the development of this disease more than 88% even at a concentration of 125 μg mL⁻¹. In addition, ciryneol C effectively suppressed barley powdery mildew. This is the first report on the antifungal activities of the three polyacetylenes from roots of C. japonicum against plant pathogenic fungi. Polyacetylenes from roots of C. japonicum may contribute to the development of environmentally safer alternatives to protect crops from various phytopathogenic fungi.     

Synergistic interaction of tea saponin with mancozeb against Pestalotiopsis theae

Tea gray blight, caused by the fungus Pestalotiopsis theae, is one of the most destructive diseases in tea plants. In this study, we evaluated the individual and synergistic antifungal activities of tea saponin (TS) and mancozeb against P. theae, as well as the mechanisms underlying their activity. The results indicated that TS significantly inhibited both the mycelial growth of P. theae, at an EC₅₀ value of 1.03 mg mL⁻¹, and its spore germination, at an EC₅₀ value of 3.68 mg mL⁻¹. TS also significantly enhanced the antifungal activity of mancozeb, and the cotoxicity factor (CTF) assays revealed that there was a synergistic interaction between TP and mancozeb (3:7) against mycelial growth and spore germination, with CTC values exceeding 100. Our results also revealed that TS and mancozeb treatments damaged the cell membranes of P. theae, leading to a significant leakage of soluble protein, reduction of sugar and induction of a significant increase of chitinase activity in the mycelial cells; the combination treatment significantly enhanced the observed damage, leakage and induction. These findings suggested that TS had antifungal activity and a synergistic effect with mancozeb and that the mechanism of this activity might be membrane damage and the consequent cytoplasm leakage.     

Gageostatins A–C,Antimicrobial Linear Lipopeptides from a Marine Bacillus subtilis

Concerning the requirements of effective drug candidates to combat against high rising multidrug resistant pathogens, we isolated three new linear lipopeptides, gageostatins A–C (1–3), consisting of hepta-peptides and new 3-β-hydroxy fatty acids from the fermentation broth of a marine-derived bacterium Bacillus subtilis. Their structures were elucidated by analyzing a combination of extensive 1D, 2D NMR spectroscopic data and high resolution ESIMS data. Fatty acids, namely 3-β-hydroxy-11-methyltridecanoic and 3-β-hydroxy-9,11-dimethyltridecanoic acids were characterized in lipopeptides 1 and 2, respectively, whereas an unsaturated fatty acid (E)-7,9-dimethylundec-2-enoic acid was assigned in 3. The 3R configuration of the stereocenter of 3-β-hydroxy fatty acids in 1 and 2 was established by Mosher’s MTPA method. The absolute stereochemistry of amino acid residues in 1–3 was ascertained by acid hydrolysis followed by Marfey’s derivatization studies. Gageostatins 1–3 exhibited good antifungal activities with MICs values of 4–32 µg/mL when tested against pathogenic fungi (R. solani, B. cinerea and C. acutatum) and moderate antibacterial activity against bacteria (B. subtilis, S. aeureus, S. typhi and P. aeruginosa) with MICs values of 8–64 µg/mL. Futhermore, gageostatins 1–3 displayed cytotoxicity against six human cancer cell lines with GI₅₀ values of 4.6–19.6 µg/mL. It is also noteworthy that mixed compounds 1+2 displayed better antifungal and cytotoxic activities than individuals.     

New Prenylxanthones from the Deep-Sea Derived Fungus Emericella sp. SCSIO 05240

Four new prenylxanthones, emerixanthones A–D (1–4), together with six known analogues (5–10), were isolated from the culture of the deep-sea sediment derived fungus Emericella sp. SCSIO 05240, which was identified on the basis of morphology and ITS sequence analysis. The newstructures were determined by NMR (¹H, ¹³C NMR, HSQC, HMBC, and ¹H-¹H COSY), MS, CD, and optical rotation analysis. The absolute configuration of prenylxanthone skeleton was also confirmed by the X-ray crystallographic analysis. Compounds 1 and 3 showed weak antibacterial activities, and 4 displayed mild antifungal activities against agricultural pathogens.     

Antifungal activity of flavonoids from Heteropterys byrsonimifolia and a commercial source against Aspergillus ochraceus: In silico interactions of these compounds with a protein kinase

To contribute to the development of new methods to reduce the contamination of coffee beans with Aspergillus ochraceus and ochratoxin A, a toxin produced by this fungus, the present work initially aimed to select plant extracts active against A. ochraceus. Among the extracts from 43 plant species, the most active was the one obtained from leaves of Heteropterys byrsonimifolia. This extract was subjected to a fractionation process that resulted in the purification of four flavonoids, among which the most active against the fungus was rutin, which presented a minimal inhibitory concentration (MIC, 32.5 μg/mL) close to the value obtained for the commercial fungicide benzalkonium chloride (7.84 μg/mL). In vitro studies with the isolated flavonoids and other four from commercial sources showed that the MIC for the flavonoid chrysin is equal to that observed for rutin, and results from an in silico study suggested that these flavonoids act against A. ochraceus by binding to a protein kinase produced by this fungus. Consequently, this enzyme and the studied flavonoids are potentially useful for the development of new products to control A. ochraceus in coffee beans.     

Combination effect of chitosan and methyl jasmonate on controlling Alternaria alternata and enhancing activity of cherry tomato fruit defense mechanisms

The effect of chitosan treatment alone or in combination with methyl jasmonate (MeJA) against Alternaria alternata in vitro and in vivo, and defense related enzyme activities were investigated. 100–500 μl/l MeJA significantly inhibited mycelial growth of A. alternata. The inhibitory activity of MeJA on mycelial growth, spore production, spore germination and germ tube length of A. alternata in vitro could be enhanced by 0.1% chitosan. The combination of 0.1% chitosan and 500 μl/l methyl jasmonate was more effective to reduce the disease incidence and lesion diameter of postharvest decay of cherry tomato than the application of MeJA or chitosan alone. The combined treatments resulted in higher activities of PPO (polyphenol oxidase), POD (peroxidase) and PAL (phenylalanine ammonialyase) than the control. This work indicated that the combination of chitosan and methyl jasmonate is a promising method to control postharvest decays of fruit and vegetables.     

Effect of additives on flavonoids, d-chiro-Inositol and trypsin inhibitor during the germination of tartary buckwheat seeds

In this study, we evaluated tartary buckwheat during germination to provide an effective process that can lead to a rapid accumulation of both the total flavonoids and d-chiro-Inositol (DCI), as well as the elimination of trypsin inhibitor activity. At different concentrations of Al³⁺, Cu²⁺, and Zn²⁺, we found significant differences of the total flavonoids and DCI accumulation, and we observed changes in phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI), and α-Galactosidase (α-Gal) activities in germinated tartary buckwheat (p < 0.05). Correlation analysis between these enzymes (PAL, CHI and α-Gal) activities and the total flavonoids and DCI contents revealed a significant correlation in germinated tartary buckwheat. The maximum accumulation of the total flavonoids and DCI were 1315.52 mg/100 g DW and 60.46 mg/g DW with the addition of Al³⁺, 1315.41 and 63.59 with the addition of Cu²⁺, and 1189.42 and 53.10 with the addition of Zn²⁺. In these metal-treated samples, both total flavonoids and DCI were significantly higher than in the control (p < 0.05). Moreover, the metallic additives at the optimum concentration had no influence on total protein content, whereas a lower trypsin inhibitor activity was observed in correlation with higher protein digestibility.     

New Cyclic Lipopeptides of the Iturin Class Produced by Saltern-Derived Bacillus sp. KCB14S006

Salterns, one of the most extreme natural hypersaline environments, are a rich source of halophilic and halotolerant microorganisms, but they remain largely underexplored ecological niches in the discovery of bioactive secondary metabolites. In continued efforts to investigate the metabolic potential of microbial populations from chemically underexplored sites, three new lipopeptides named iturin F₁, iturin F₂ and iturin A₉ (1–3), along with iturin A₈ (4), were isolated from Bacillus sp. KCB14S006 derived from a saltern. The structures of the isolated compounds were established by 1D-, 2D-NMR and HR-ESIMS, and their absolute configurations were determined by applying advanced Marfey’s method and CD spectroscopy. All isolates exhibited significant antifungal activities against various pathogenic fungi and moderate cytotoxic activities toward HeLa and src^ts-NRK cell lines. Moreover, in an in vitro enzymatic assay, compound 4 showed a significant inhibitory activity against indoleamine 2,3-dioxygenase.     

(±)-Pestalachloride D,an Antibacterial Racemate of Chlorinated Benzophenone Derivative from a Soft Coral-Derived Fungus Pestalotiopsis sp

A new antibacterial chlorinated benzophenone derivative, (±)-pestalachloride D (1), along with a related analog, (±)-pestalachloride C (2), was recently isolated from the marine-derived fungus Pestalotiopsis sp. isolated from a soft coral Sarcophyton sp. collected from Yongxing Island in the South China Sea. Both chiral HPLC analysis and single-crystal X-ray data indicated that 1 is a racemic mixture. Interestingly, 1 did not exhibit any effect in the zebrafish embryo teratogenicity assay, while 2 led to abnormal growth. The potential impact on zebrafish embryo growth is discussed based on their crystal structures. The main difference of crystal structures between 1 and 2 is that the six-member non-aromatic ring (O4, C10, C9, C8, C2′, and C3′) in 1 exhibits a distorted chair conformation, while 2 shows a distorted boat conformation. Moreover, compounds 1 and 2 both exhibited moderate antibacterial activity.     

Effect of genotype and environment on flavonoid concentration and profile of black sorghum grains

In recent years, colored sorghum genotypes high in flavonoids have been developed. Flavonoid levels of eight black sorghum genotypes grown in four locations in Texas were evaluated to assess the relative genotype, environment and genotype × environment effects. Levels of total 3-deoxyanthocyanidins ranged from 292 μg/g to 499 μg/g and 251 μg/g to 804 μg/g across environments and genotypes, respectively. Total 3-deoxyanthocyanidins in sorghums from Halfway were low (178–694 μg/g) due to the reduction of their non-methoxylated forms. This reduction is likely due to significant grain weathering which was observed only at Halfway. In addition, flavanone and flavone levels were the lowest at Halfway with levels of 12 μg/g and 78 μg/g, respectively. For all flavonoids there was a genotype by environment interaction (p < 0.01) which suggests that environment had a different effect on flavonoid levels depending on the genotype. Color values L*, a* and b* did not correlate with flavonoid content. Due to genotype, environment and their interactions, sorghum breeders must evaluate these traits in multiple environments to identify genotypes with high and stable production of flavonoid compounds.     

Antagonistic yeasts with potential to control Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. and Colletotrichum acutatum J.H. Simmonds on avocado fruits

Avocado is an economically important fruit that is severely affected by anthracnose disease due to the infection with Colletotrichum spp. In this study, avocado fruits with anthracnose symptoms were collected in Morelos, Mexico. Two phytopathogenic fungi were isolated from these fruits and identified as Colletotrichum gloeosporioides and Colletotrichum acutatum using ITS sequences. Further, eleven yeasts from avocado (three from fruits, four from leaves and four from rhizospheric soil) were isolated; of which three showed in vitro antagonistic activity against C. gloeosporioides and C. acutatum. ITS sequence analysis of the isolated yeasts revealed that the strains obtained from fruits belonged to Candida intermedia while those isolated from leaves belonged to Wickerhamomyces anomalus. C. intermedia reduced disease incidence caused only by C. gloeosporioides, whereas, W. anomalus caused a significant reduction in the incidence and severity of disease caused by both C. gloeosporioides and C. acutatum. To the best of our knowledge, this is the first report on the antagonistic activity of W. anomalus or C. intermedia against Colletotrichum acutatum. Thus, W. anomalus is a potential natural alternative for controlling anthracnose infection and associated loss in avocado crops.     

Comparative assessment of antioxidant and cholinesterase inhibitory properties of the marigold extracts from Calendula arvensis L. and Calendula officinalis L.

Calendula sp. is an important medicinal and industrial plant with various bioactivities. In this study, we examined enzyme inhibitory effects of the n-hexane, dichloromethane, acetone, ethyl acetate, methanol, and water extracts of the leaf and flowers of Calendula arvensis L. and C. officinalis L. against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The extracts were screened for their antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric ion-chelating capacity and ferric-reducing antioxidant power (FRAP) assays at 250, 500, and 1000 μg mL⁻¹. Total phenol and flavonoid quantification of the extracts was achieved using Folin-Ciocalteau and AlCl₃ reagents, respectively. The ethyl acetate extract of C. arvensis flowers was the most active in AChE inhibition assay (31.24 ± 1.29%), while the n-hexane extract of C. officinalis leaves exerted the highest ferric ion-chelating capacity (74.27 ± 2.25%). Thin layer chromatographic analysis indicated presence of flavonoid and triterpene derivatives mainly in the extracts.     

Antifungal activity in vitro of Flourensia spp. extracts on Alternaria sp., Rhizoctonia solani,and Fusarium oxysporum

There are 32 species of Flourensia genus with 9 native to Mexico. These species contain compounds with potential use for pest control. In this paper, we report the antifungal activities of ethanol extracts from three endemic species in Coahuila state: Flourensia microphylla, Flourensia cernua, and Flourensia retinophylla. Also, preliminary information on the chemical composition of the extracts is included. Antifungal activity was tested against three pathogens attacking commercial crops: Alternaria sp., Rhizoctonia solani, and Fusarium oxysporum. The extracts concentration varied from 10 to 1500 μl l⁻¹. The ANOVA showed highly significant differences (P ≤ 0.01) with the extracts, the doses, and on the interaction extract × dose. Inhibition effect was observed from 10 μl l⁻¹ in all three species. Total inhibition was found only with F. cernua and F. retinophylla at 1000 μl l⁻¹ for R. solani, the three species inhibited the three pathogens at 1500 μl l⁻¹. Infrared analysis showed similar absorption signals for the extracts of the three species although in different concentration. This suggests that similar compounds may be present. The control of these pathogens by natural compounds is interesting both for environmental and economic reasons. The use of semiarid lands plants may improve the socioeconomic level of the people within the region.     

Antifungal activities of extracts produced by liquid fermentations of Chilean Stereum species against Botrytis cinerea (grey mould agent)

Extracts obtained from liquid mycelial fermentations of Chilean species of the Stereum genus showed antifungal activity against Botrytis cinerea. Thirty-six strains were evaluated in vivo and in vitro assays, 25 belonging to Stereum hirsutum (Sh) and 11 to Stereum rameale (Sr). Two types of extracts were obtained: EtOAc-extract (liquid phase) and MeOH-extract (mycelial phase). Plate diffusion assay showed that EtOAc-extracts were more active than MeOH-extracts. S. hirsutum included 4 strains with the highest antifungal activity (Sh134-11, Sh144-11, Sh152-11, Sh155-11) and S. rameale highlighted with two strains (Sr25-11, Sr27-11). Effects on the mycelial growth of B. cinerea showed that EtOAc-extracts produced by S. hirsutum (Sh134-11, Sh152-11) inhibited from 1000 μg mL⁻¹, reaching 67 and 49%, respectively. At 2000 μg mL⁻¹, these strains inhibited nearly 80% of mycelial growth. EtOAc-extract of Sh134-11 was more effective to control the sporogenesis, inhibiting in 100% the sporulation at 500 μg mL⁻¹. Assays showed that Sh134-11 and Sh152-11 exhibited a minimal fungicidal concentration (MFC) of 50 and 100 μg mL⁻¹ respectively and minimal inhibitory concentration (MIC) at 20 μg mL⁻¹. EtOAc-extracts of Sr25-11 and Sr27-11 showed MFC value at 100 μg mL⁻¹ and MIC at 20 and 50 μg mL⁻¹, respectively. Strawberries treated with 1000 μg mL⁻¹of Sh134-11 and Sr25-11 reached 82 and 72% of decay inhibition, respectively. Treatments with 2000 μg mL⁻¹ showed a decay inhibition of 90% approximately. In vivo tests are in accordance with the results obtained in vitro assays, confirming the efficacy of Sh134-11 and Sr25-11 to control B. cinerea. Differences in antifungal activities observed in the different strains suggested that the ability to produce bioactive compounds is not homogenously distributed among S. hirsutum and S. rameale. Our study would suggest that submerged fermentations of Chilean S. hirsutum strain Sh134-11 produce extracts, which could be used as possible biofungicides and an alternative to synthetic fungicides.     

Pestalotioid fungi from Restionaceae in the Cape Floral Kingdom

Eight pestalotioid fungi were isolated from the Restionaceae growing in the Cape Floral Kingdom of South Africa. Sarcostroma restionis, Truncatella megaspora, T. restionacearum and T. spadicea are newly described. New records include Pestalotiopsis matildae, Sarcostroma lomatiae, Truncatella betulae and T. hartigii. To resolve generic affiliations, phylogenetic analyses were performed on ITS (ITS1, 5.8S, ITS2) and part of 28S rDNA. DNA data support the original generic concept of Truncatella, which encompasses Pestalotiopsis species having 3-septate conidia. The genus Sarcostroma is retained as separate from Seimatosporium.Taxonomic novelties: Pestalotiopsis matildae (Richatt) S. Lee & Crous comb. nov., Truncatella betulae (Morochk.) S. Lee& Crous comb. nov., Sarcostroma restionis S. Lee & Crous sp. nov., Truncatella megaspora S. Lee & Crous sp. nov., Truncatella restionacearum S. Lee & Crous sp. nov., Truncatella spadicea S. Lee & Crous sp. nov.     

Fungal diseases of spring wheat in central Saudi Arabia

Fungal diseases of spring wheat (Triticum aestivum L.) in Central Saudi Arabia (AlGassim region) were surveyed in 1984 and 1985. Over 95% of the wheat fields were planted to the Yecora Rojo cultivar. Root and crown rots (Fusarium spp. and Helminthosporium spp.); brown root rot (Pythium spp.); leaf and head blotches (Helminthosporium spp.) and take-all (Gaeumannomyces sp.) were the most serious fungal diseases observed in the fields. Several H. sativum isolates were pathogenic to seedling leaves of most or all local and imported wheat cultivars (22 cultivars). Numerous soil-borne fungi were isolated from wheat roots and tested for pathogenicity to Yecora Rojo seedlings in the greenhouse. Alternaria sp., Helminthosporium spp. (two isolates), Fusarium spp. (three isolates), Pythium spp., Stemphylium spp. (two isolates) and Gaeumannomyces sp. were pathogenic to the inoculated wheat plants in the greenhouse.     

Bioactive Indole Diketopiperazine Alkaloids from the Marine Endophytic Fungus Aspergillus sp. YJ191021

Six new prenylated indole diketopiperazine alkaloids, asperthrins A–F (1–6), along with eight known analogues (7–14), were isolated from the marine-derived endophytic fungus Aspergillus sp. YJ191021. Their planar structures and absolute configurations were elucidated by HR-ESI-MS, 1D/2D NMR data, and time-dependent density functional theory (TDDFT)/ECD calculation. The isolated compounds were assayed for their inhibition against three agricultural pathogenic fungi, four fish pathogenic bacteria, and two agricultural pathogenic bacteria. Compound 1 exhibited moderate antifungal and antibacterial activities against Vibrio anguillarum, Xanthomonas oryzae pv. Oryzicola, and Rhizoctonia solani with minimal inhibitory concentration (MIC) values of 8, 12.5, and 25 μg/mL, respectively. Furthermore, 1 displayed notable anti-inflammatory activity with IC₅₀ value of 1.46 ± 0.21 μM in Propionibacterium acnes induced human monocyte cell line (THP-1).     

Efficacy of Lawsonia inermis leaves extract and its phenolic compounds against olive knot and crown gall diseases

This study was undertaken to determine the antibacterial efficacy of the leaves extracts of Lawsonia inermis in vitro and in vivo, against the phytopathogenic bacteria Pseudomonas savastanoi pv savastanoi IVIA 1628 and Agrobacterium tumefaciens. The hydroalcoholic extract of L. inermis was fractionated by liquid–liquid partition using hexane, chloroform, ethyl acetate and butanol. Among the tested fractions, the ethyl acetate (EtOAcF) and chloroform (CHCl₃F) extracts exhibited high inhibition against all tested plant pathogens. The extracts exerted a bactericidal activity against both P. savastanoi and A. tumefaciens with MIC values ranging from 1.25 to 2.5 mg/ml. In planta experiments, the EtOAcF, tested at four concentrations (0.4, 0.2, 0.1 and 0.05 mg/wounds), completely inhibited the formation of knots on twigs of olive and tomato plants inoculated with pathogenic strains of P. savastanoi and A. tumefaciens (strains B6 and C58). The phytochemical screening revealed that the L. inermis fractions contain flavonoids, quinones, tannins and terpenoids. The qualitative analysis of the EtOAcF by LC–DAD–ELSD–ESI/MSⁿ showed the presence of eight identified phenolic and phenolic glycoside compounds. These results suggest that L. inermis extracts could be used to control plant bacterial diseases caused by P. savastanoi and A. tumefaciens.     

Antifungal activity of leaf extracts from South African trees against plant pathogens

The antifungal activity of acetone, methanol, hexane and dichloromethane leaf extracts of six plant species (Bucida buceras, Breonadia salicina, Harpephyllum caffrum, Olinia ventosa, Vangueria infausta and Xylotheca kraussiana) were evaluated for antifungal activity against seven plant pathogenic fungal species (Aspergillus niger, Aspergillus parasiticus, Colletotricum gloeosporioides, Penicillium janthinellum, Penicillium expansum, Trichoderma harzianum and Fusarium oxysporum). These plant species were selected from 600 evaluated inter alia, against two animal fungal pathogens. All plant extracts were active against the selected plant pathogenic fungi. Of the six plant species, B. buceras had the best antifungal activity against four of the fungi, with minimum inhibitory concentration (MIC) values as low as 0.02 mg/ml and 0.08 mg/ml against P. expansum, P. janthinellum, T. harzianum and F. oxysporum. Some of the plant extracts had moderate to low activity against other fungi, indicating that the activity is not based on a general metabolic toxicity. P. janthinellum, T. harzianum and F. oxysporum were the most sensitive fungal species, with a mean MIC of 0.28 mg/ml, while the remaining four fungi were more resistant to the extracts tested, with mean MICs above 1 mg/ml. The number of active compounds in the plant extracts was determined using bioautography with the listed plant pathogens. No active compounds were observed in some plant extracts with good antifungal activity as a mixture against the fungal plant pathogens, indicating possible synergism between the separated metabolites, B. salicina and O. ventosa were the most promising plant species, with at least three antifungal compounds. Leaf extracts of different plant species using different methods (acetone, hexane, DCM and methanol) had antifungal compounds with the same R_f values. The same compounds may be responsible for activity in extracts of different plant species. Based on the antifungal activity, crude plant extracts may be a cost effective way of protecting crops against fungal pathogens. Because plant extracts contain several antifungal compounds, the development of resistant pathogens may be delayed.