Anti-oomycete Activity Research Articles

Comparative genomic and metabolomic study of three Streptomyces sp. differing in biological activity.

The Streptomyces genus is known to produce many specialized metabolites of value for medicine, but the potential of these metabolites in agronomy remains largely unexplored. In this study, we investigated three phylogenetically closely related Streptomyces strains (B5, B91, and B135) isolated from three distinct soil samples in Sudan. Despite belonging to the same species, these strains exhibited different ranges of Phytophthora infestans inhibition. The objective of this work was to identify the active compound(s) responsible for the inhibition of P. infestans and of other plant pathogens by comparing the genomes and metabolomes of the three strains which showed distinct activity patterns: B5 was the strongest inhibitor of oomycetes, B5 and B91 both inhibited most fungi and B135 was the only strain showing antibacterial activity. Our comparative genomic and metabolomic analysis identified borrelidin as the bioactive compound underlying B5's strong anti-oomycete activity and highlighted a few other metabolites as putative candidates underlying the strains' antifungal and antibacterial activities. This study illustrates the power of comparative genomics and metabolomics on phylogenetically closely related strains of differing activities to highlight bioactive compounds that could contribute to new sustainable crop protection strategies.

Harnessing Plant’s Arsenal: Essential Oils as Promising Tools for Sustainable Management of Potato Late Blight Disease Caused by Phytophthora infestans—A Comprehensive Review

Potato late blight disease is caused by the oomycete Phytophthora infestans and is listed as one of the most severe phytopathologies on Earth. The current environmental issues require new methods of pest management. For that reason, plant secondary metabolites and, in particular, essential oils (EOs) have demonstrated promising potential as pesticide alternatives. This review presents the up-to-date work accomplished using EOs against P. infestans at various experimental scales, from in vitro to in vivo. Additionally, some cellular mechanisms of action on Phytophthora spp., especially towards cell membranes, are also presented for a better understanding of anti-oomycete activities. Finally, some challenges and constraints encountered for the development of EOs-based biopesticides are highlighted.

Anti-oomycete activities from essential oils and their major compounds on Phytophthora infestans

Botanicals are various plant-based products like plant extracts or essential oils. Anti-fungal activities of selected essential oils were tested on the pathogen causing potato and tomato late blight (Phytophthora infestans). Tests to evaluate anti-oomycete activities of commercial essential oils and their major compounds were carried out in vitro in microplate in liquid media. Anti-oomycete activities on Phytophthora infestans strain were obtained from essential oils/major compounds: Eucalyptus citriodora/citronellal; Syzygium aromaticum (clove)/eugenol; Mentha spicata/D-Carvone, L-Carvone; Origanum compactum/carvacrol; Satureja montana (savory)/carvacrol; Melaleuca alternifolia (tea tree)/terpinen-4-ol, and Thymus vulgaris/thymol. As an active substance of mineral origin, copper sulfate was chosen as a control. All selected essential oils showed an anti-oomycete activity calculated with IC50 indicator. The essential oils of clove, savory, and thyme showed the best anti-oomycete activities similar to copper sulfate, while oregano, eucalyptus, mint, and tea tree essential oils exhibited significantly weaker activities than copper sulfate. Clove essential oil showed the best activity (IC50 = 28 mg/L), while tea tree essential oil showed the worst activity (IC50 = 476 mg/L). For major compounds, three results were obtained: they were statistically more active than their essential oils (carvacrol for oregano, D- and L-Carvone for mint) or as active as their essential oils sources (thymol for thyme, carvacrol for savory, terpinen-4-ol for tea tree) or less active than their original essential oils (eugenol for clove, citronellal for eucalyptus). Microscopical observations carried out with the seven essential oils showed that they were all responsible for a modification of the morphology of the mycelium. The results demonstrated that various essential oils show different anti-oomycete activities, sometimes related to a major compound and sometimes unrelated, indicating that other compounds must play a role in total anti-oomycete activity.

Isolation of two triterpenoids from Phlomis purpurea, one of them with anti-oomycete activity against Phytophthora cinnamomi, and insights into its biosynthetic pathway.

Phytophthora cinnamomi is an important plant pathogen responsible for dieback diseases in plant genera including Quercus, Fagus, Castanea, Eucalyptus, and Pinus, among others, all over the world. P. cinnamomi infection exerts tremendous ecological and economic losses. Several strategies have been developed to combat this pathogenic oomycete, including the search for novel anti-oomycete compounds. In this work, a Mediterranean vascular plant, Phlomis purpurea, has been screened for secondary bioactivity against this pathogen. The genus Phlomis includes a group of herbaceous plants and shrubs described as producers of many different bioactive compounds, including several triterpenoids. Triterpenoids are well-known molecules synthesized by plants and microorganisms with potent antioxidant, antitumoral, and antimicrobial activities. We have isolated by HPLC-DAD and characterized by HPLC-MS and NMR two nortriterpenoid compounds (phlomispentaol A and phlomispurtetraolone) from the root extracts of P. purpurea. One of them (phlomispentaol A) is active against the plant pathogenic oomycete P. cinnamomi (based on in vitro inhibition bioassays). Based on their chemical structure and their relationship to other plant triterpenoids, oleanolic acid is proposed to be the common precursor for these molecules. The anti-oomycete activity shown by phlomispentaol A represents a promising alternative to counteract the worldwide-scale damage caused to forest ecosystems by this pathogen.

PGPR control Phytophthora capsici in tomato through induced systemic resistance, early hypersensitive response and direct antagonism in a cultivar-specific manner

Plant pathogens cause significant crop losses worldwide and present significant challenges to reliable food systems. The hemibiotroph Phytophthora capsici is ranked within the top 10 most problematic oomycete plant pathogens. P. capsici induces significant damage to plants by causing root rot, stem blight, and fruit rot, leading to decreased crop yields, economic losses, and increased plant susceptibility to secondary infections. The current study tested the hypothesis that plant growth promoting rhizobacteria (PGPR), namely Bacillus velezensis UQ9000N and Pseudomonas azotoformans UQ4510An, have inhibitory effects against various fungi and oomycetes. This study also hypothesised that the plant genotype affects the capability of UQ4510An to control P. capsici infection. Our results revealed that B. velezensis UQ9000N and P. azotoformans UQ4510An inhibited the growth of several plant pathogens by 50% or higher. These bacteria also induced abnormal mycelial morphology of P. capsici and Fusarium oxysporum f. sp. lycopersici. Moreover, P. azotoformans UQ4510An exhibited anti-oomycete activity in vitro and in planta, by reducing symptoms of P. capsici infection in various tomato plant cultivars in a genotype-dependent manner. Some tomato cultivars which presented less improvements of phenotypic parameters from the UQ4510An inoculation in the absence of the pathogen had a more pronounced reduction in symptoms upon P. capsici infection. Furthermore, our results indicated that the main biocontrol mechanism of P. azotoformans UQ4510An against P. capsici is a combination of direct antagonism and induction of induced systemic resistance (ISR) involving a hypersensitive response (HR) in the plant host at early stages of infection.

Assessment of Antifungal/Anti-Oomycete Activity of Frass Derived from Black Soldier Fly Larvae to Control Plant Pathogens in Horticulture: Involvement of Bacillus velezensis

Frass, the residual material resulting from the bioconversion of organic matter by black soldier fly larvae (BSFL), has gained attention as a sustainable alternative to conventional fertilizers due to its high nutrient content. Additionally, frass has been found to possess antifungal properties, which can help control plant pathogens affecting horticultural crops. In this study, frass from BSFL reared on the Gainesville diet, a universally employed reference/control diet, was investigated in vitro for its effect on the growth of seven important fungal/oomycete pathogens. Dual culture overlay assays clearly showed that fresh Gainesville diet extract, as well as BSFL frass extract derived from this diet, contained microorganisms producing compound(s) that strongly inhibit(s) the mycelial growth of fungal/oomycete plant pathogens. Fungi and bacteria were then isolated from the fresh Gainesville diet and BSFL frass using the serial dilution technique. Among the different fungi/bacteria isolated, the isolate GV1-11 in Gainesville diet and FGV15-6 in frass demonstrated strong antifungal/anti-oomycete activity. Both isolates were genetically identified by whole-genome sequencing as Bacillus velezensis, a bacterium used as a biocontrol agent, strongly suggesting that B. velezensis, which is present in the Gainesville diet, can survive the process of BSFL rearing and is one of the key factors contributing to the observed antifungal and anti-oomycete activity in the resulting frass. This work underlines the importance of the inherent microbial characteristics of feedstocks on the antifungal/anti-oomycete activity of frass and points out the possibility of exploiting frass to control plant pathogens affecting horticultural crops.

Synthesis, Anti-Oomycete and Anti-fungal Activities of Novel Cinchona Alkaloid Derivatives Containing Sulfonate Moiety.

Using cinchona alkaloid as the lead compound, twenty-four cinchona alkaloid sulfonate derivatives (1 a-l, 2 a-c, 3 a-c, 4 a-c, and 5 a-c) were designed and prepared by modifying their C9 position, and structurally confirmed by 1 H-NMR, 13 C-NMR, HR-MS and melting points. Moreover, the stereochemical configurations of compounds 1 f and 1 l were unambiguously confirmed by single-crystal X-ray diffraction. Furthermore, we determined the anti-oomycete and anti-fungal activities of these target compounds against Phytophthora capsici and Fusarium graminearum in vitro. The results showed that two compounds 4 b and 4 c exhibited prominent anti-oomycete activity, and the median effective concentration (EC50 ) values of 4 b and 4 c against P. capsici were 22.55 and 16.32 mg/L, respectively. This study suggested that when the C9 position of cinchona alkaloid sulfonate derivatives is in the S configuration and the 6'-position methoxy group is not present, the anti-oomycete activity is superior. In addition, five compounds 1 e, 1 f, 1 k, 3 c and 4 c displayed significant anti-fungal activity, with EC50 values of 43.64, 45.07, 80.18, 48.58 and 41.88 mg/L against F. graminearum, respectively. This result indicates that only when a specific substituent is introduced into the structural framework of the target compound, the corresponding compound exhibits significant inhibitory activity against fungi.

Synthesis, anti-oomycete and anti-fungal activities of novel cinchona alkaloid derivatives bearing carbamate moiety

In order to explore novel natural product-based anti-oomycete and anti-fungal agents, twenty cinchona alkaloid carbamate derivatives (1a-d, 2a-d, 3a-d, 4a-d, and 5a-d) were designed and prepared, and structurally confirmed by 1H NMR, 13C NMR, HRMS, and melting point. The stereochemical configuration of compound 1a was unambiguously confirmed by single-crystal X-ray diffraction. Furthermore, we evaluated the anti-oomycete and anti-fungal activities of these target compounds against Phytophthora capsici and Fusarium graminearum in vitro. The results showed that five compounds 1d, 2d, 3d, 4d, and 5d exhibited prominent anti-oomycete and anti-fungal activities, and the median effective concentration (EC50) values of 1d, 2d, 3d, 4d, and 5d against P. capsici and F. graminearum were 21.1, 16.6, 22.4, 14.4, 13.9 mg/L and 38.2, 19.8, 36.6, 30.3, 27.7 mg/L, respectively. This study suggested that when a specific substituent is introduced into the cinchona alkaloid skeleton, i.e. R1/R2 = Ph/Ph, the corresponding derivatives exhibit significant anti-oomycete and anti-fungal activities. And the configuration of the C8/9 position of the target compound is crucial for its anti-oomycete and anti-fungal activities, and 9S-configuration is optimal.

Chemical Constituents and Antimicrobial Activity of a Ganoderma lucidum (Curtis.) P. Karst. Aqueous Ammonia Extract.

Mushroom extracts have shown potential as a source of new antimicrobial agents. This study investigates the chemical profile of an aqueous ammonia extract obtained from the carpophores of Ganoderma lucidum, which grows on Quercus ilex trees, and explores its valorization as a biorational. The major chemical constituents of the extract, identified through gas chromatography-mass spectrometry, include acetamide, oleic acid, 1,2,3,4-butanetetrol, monomethyl azelate, undecane, and palmitic acid. The anti-oomycete and antifungal activity of G. lucidum extract was evaluated against Phytophthora cinnamomi, the primary threat to Quercus spp. in the dehesa biome, as well as three Botryosphaeriaceae fungi. In vitro tests revealed minimum inhibitory concentration (MIC) values of 187.5 μg·mL-1 against P. cinnamomi and 187.5-1000 μg·mL-1 against the fungi. Furthermore, conjugation of the G. lucidum extract with chitosan oligomers (COS) synergistically enhanced its antimicrobial activity, resulting in MIC values of 78.12 and 375-500 μg·mL-1 against P. cinnamomi and the fungi, respectively. These MIC values are among the highest reported to date for natural products against these phytopathogens. Subsequent ex situ testing of the COS-G. lucidum conjugate complex on artificially inoculated Q. ilex excised stems resulted in high protection against P. cinnamomi at a dose of 782 µg·mL-1. These findings support the potential utilization of this resource from the dehesa ecosystem to protect the holm oak, aligning with sustainable and circular economy approaches.

Semisynthesis, anti-oomycete and anti-fungal activities of ursolic acid ester derivatives

Using ursolic acid (UA) as the lead compound, thirteen UA ester derivatives (3 and 7a-l) were synthesized by modifying their C-3 and C-28 positions, respectively, and their structures were well characterized by 1H NMR, 13C NMR, HRMS and melting points. Furthermore, we evaluated the anti-oomycete and anti-fungal activities of these compounds against Phytophthora capsici and Fusarium graminearum in vitro. The results showed that compound 7h exhibited prominent anti-oomycete and anti-fungal activities, and the median effective concentration (EC50) values of 7h against P. capsici and F. graminearum were 70.49 and 113.21 mg/L, respectively. This study suggested that the anti-oomycete and anti-fungal activities of esters synthesized by introducing acyloxy group at C-3 position of UA was more conspicuous than that of esters synthesized by introducing benzyloxy group at C-28 position. This result will pave the way for further modification of UA to develop potential new fungicides.

Design, Synthesis, and Antifungal/Antioomycete Activity of Thiohydantoin Analogues Containing Spirocyclic Butenolide.

Novel fungicidal agents were designed based on the combination of two privileged scaffolds, thiohydantoin and spirocyclic butenolide, which are widely found in natural products. The synthesized compounds were characterized by 1H NMR, 13C NMR, and high-resolution electrospray ionisation mass spectrometry. The in vitro antioomycete activity evaluation showed that most of the compounds exhibited excellent inhibitory activities against different developmental stages in the life cycle of pathogenic oomycete Phytophthora capsici. Compound 5j could inhibit the mycelial growth, sporangium production, zoospore release, and cystospore germination significantly with EC50 values of 0.38, 0.25, 0.11, and 0.026 μg/mL, respectively. The in vivo antifungal/antioomycete bioassay results revealed that the series of compounds generally showed outstanding control efficacies against the pathogenic oomycete Pseudoperonospora cubensis, and compounds 5j, 5l, 7j, 7k, and 7l possessed broad-spectrum antifungal activities against the test phytopathogens. The in vivo protective and curative efficacies against P. capsici of the representative compound 5j were excellent, which were better than those of azoxystrobin. More prominently, 5j significantly promoted the biomass accumulation of the root system and reinforced the cell wall by callose deposition. The pronounced upregulation of immune response-related genes indicated that the active oomycete inhibitor 5j also functioned as a plant elicitor. Transmission electron microscopy observation and the enzyme activity test demonstrated that the mechanism of action of 5j was to bind to the pivotal protein, complex III on the respiratory chain, which resulted in a shortage of energy supply. Molecular docking results exhibited that compound 5j appropriately matched with the Qo pocket and had no interaction with the most commonly mutated site Gly-142, which may be of significant benefit in Qo fungicide resistance management. Compound 5j showed great advantages and potential in oomycete control, resistance management, and induction of disease resistance. A further investigation of 5j with a unique structure might have direct implications for the creation of novel oomycete inhibitors against plant-pathogenic oomycetes.

Synthesis, anti-oomycete activity of 1-sulfonyloxy/acyloxysesamol derivatives

In order to explore novel natural product-based anti-oomycete agent, sixteen 1-sulfonyloxysesamol derivatives (3a-p) and fourteen 1-acyloxysesamol derivatives (5a-n) were designed and prepared, and structurally confirmed by 1H NMR, 13C NMR, HRMS, and melting point. The stereochemical configurations of compounds 3k and 5f were unambiguously confirmed by single-crystal X-ray diffraction. Moreover, we assessed the target compounds 3a-p and 5a-n as anti-oomycete activity against a serious agricultural disease of Phytophthora capsici by using the mycelial growth rate method. Among the thirty sesamol ester derivatives determined, eight compounds 3j, 3k, 3m, 3p, 5g, 5i, 5l, and 5m showed more potent anti-oomycete activity than that of the positive control zoxamide (EC50 = 23.79 mg/L), and the EC50 values of 13.80, 17.65, 11.80, 12.70, 17.71, 9.53, 21.94, and 15.43 mg/L, respectively. Especially compound 5i exhibited the best anti-oomycete activity against P. capsici with EC50 value of 9.53 mg/L. Overall, the anti-oomycete activities of 1-acyloxysesamol derivatives is higher than that of 1-sulfonyloxysesamol derivatives. It is proved that the introduction of the acyl group at hydroxyl position of sesamol is more beneficial to improve its anti-oomycete activity than that of the sulfonyl group.

Natural product 2-Phenylethanol inhibits ATP synthesis of P. infestans by blocking the oxidative phosphorylation pathway to prevent potato late blight

Potato tuber rots caused by the late blight pathogens oomycete Phytophthora infestans results in severe postharvest losses in transit and storage. Natural volatile organic compounds (VOCs) produced by antagonistic microorganisms have good biocontrol effects. However, VOCs for controlling potato late blight largely remains scarcity, the antimicrobial mechanisms were not entirely clear. In this study, an antagonistic yeast Candida quercitrusa strain Cq-1 was reported that had strong anti-oomycete activity on P. infestans. Its natural VOCs are mainly attributable to the inhibitory ability at the inhibition rate of 85.94%. Mycelial growth of P. infestans and lesions on postharvest potato tubers were inhibited after exposure to its VOCs by storage simulation assay. Furthermore, 2-Phenylethanol (C8H10O) (2-PE) was identified as one of the primary components of VOCs in C. quercitrusa through GC-MS. Hyphal growth of P. infestans following 2-PE treatment was malformed and shriveling. Mechanism investigations revealed that 2-PE blocked the oxidative phosphorylation pathway from RNA-seq analysis, the down-regulation of relevant genes was validated by qPCR, eventually causing a 68.08% reduction in ATP contents, thereby leading to ATP depletion and ultimate mortality of P. infestans. Hence, 2-PE suggesting potential application to protect postharvest potato tubers from late blight.

Synthesis, anti-oomycete and fungal activities of resveratrol sulfonate derivatives containing three esters moieties

In order to explore novel natural product-based anti-oomycete and fungal agents, thirteen unreported resveratrol sulfonate derivatives containing three esters moieties were designed and prepared using the principle of activity superposition, and structurally confirmed by 1H NMR, 13C NMR, HRMS, and m.p. Furthermore, we evaluated the target compounds (3a–m) as anti-oomycete and fungal activities against two serious agricultural diseases of Phytophthora capsici and Fusarium graminearum, respectively. Among the thirteen resveratrol sulfonate derivatives tested, three compounds 3d, 3k, and 3l exhibited the most potent anti-oomycete activity against P. capsici with EC50 values of 27.31, 27.69, and 26.14 mg/L, respectively. Moreover, two compounds 3e and 3l exhibited the most potent anti-fungal activity against F. graminearum with EC50 values of 75.81, and 73.60 mg/L, respectively. Overall, the anti-oomycete activity against P. capsici of the target compound was significantly better than that of the anti-fungal activity against F. graminearum. In particular, anti-oomycete and fungal activities showed that the structural skeleton presentation activity was closely related to the different substituents of the sulfonyloxy groups, especially the anti-oomycete activity. This study will lay a solid foundation for further modifying resveratrol to develop potential new fungicides.

Anti-Oomycete Activity and Pepper Root Colonization of Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 against Phytophthora capsici

Previously, Pseudomonas plecoglossicida YJR13 and Pseudomonas putida YJR92 from a sequential screening procedure were proven to effectively control Phytophthora blight caused by Phytophthora capsici. In this study, we further investigated the anti-oomycete activities of these strains against mycelial growth, zoospore germination, and germ tube elongation of P. capsici. We also investigated root colonization ability of the bacterial strains in square dishes, including cell motility (swimming and swarming motilities) and biofilm formation. Both strains significantly inhibited mycelial growth in liquid and solid V8 juice media and M9 minimal media, zoospore germination, and germ tube elongation compared with Bacillus vallismortis EXTN-1 (positive biocontrol strain), Sphingomonas aquatilis KU408 (negative biocontrol strain), and MgSO4 solution (untreated control). In diluted (nutrient-deficient) V8 juice broth, the tested strain populations were maintained at >108 cells/ml, simultaneously providing mycelial inhibitory activity. Additionally, these strains colonized pepper roots at a 106 cells/ml concentration for 7 days. The root colonization of the strains was supported by strong swimming and swarming activities, biofilm formation, and chemotactic activity towards exudate components (amino acids, organic acids, and sugars) of pepper roots. Collectively, these results suggest that strains YJR13 and YJR92 can effectively suppress Phytophthora blight of pepper through direct anti-oomycete activities against mycelial growth, zoospore germination and germ tube elongation. Bacterial colonization of pepper roots may be mediated by cell motility and biofilm formation together with chemotaxis to root exudates.

Diketopiperazine cyclo(-l-Leu-l-Phe) with plant elicitation activity and anti-oomycete activity against Plasmopara viticola.

The aim of this study was to contribute to the reduction of synthetic chemical fungicide application in viticulture by using cyclo(-l-Leu-l-Phe) (cLF) produced by Bacillus subtilis KS1, a candidate for biological control agent. cLF is a diketopiperazine and belongs to the family of 2,5-diketopiperazines. KS1 secreted micromolar levels of cLF into culture medium. Micromolar concentrations of cLF structure-dependently decreased by ∼90% both disease severity and lesion density of downy mildew in grapevine cultivated in a growth chamber. Microscopic observation demonstrated that cLF inhibited Plasmopara viticola haustorium formation by 80% but not zoospore germination on leas disks. Interestingly, millimolar concentrations of cLF induced plant defense response, such as expression of genes encoding chitinase and β-1,3-glucanase, in grapevine leaves through the salicylic acid and jasmonate signaling pathways. We demonstrated that cLF was a weapon against P. viticola infection. Further evaluation of cLF in field trials is required to uncover its inherent characteristics.

Synthesis of 3,4-dihydroisoquinolin-1(2H)-one derivatives and their antioomycete activity against the phytopathogen Pythium recalcitrans.

In an effort to exploit the bioactive natural scaffold 3,4-dihydroisoquinolin-1(2H)-one for plant disease management, 59 derivatives of this scaffold were synthesized using the Castagnoli-Cushman reaction. The results of bioassay indicated that their antioomycete activity against Pythium recalcitrans was superior to the antifungal activity against the other 6 phytopathogens. Compound I23 showed the highest in vitro potency against P. recalcitrans with an EC50 value of 14 μM, which was higher than that of the commercial hymexazol (37.7 μM). Moreover, I23 exhibited in vivo preventive efficacy of 75.4% at the dose of 2.0 mg/pot, which did not show significant differences compared with those of hymexazol treatments (63.9%). When the dose was 5.0 mg per pot, I23 achieved a preventive efficacy of 96.5%. The results of the physiological and biochemical analysis, the ultrastructural observation and lipidomics analysis suggested that the mode of action of I23 might be the disruption of the biological membrane systems of P. recalcitrans. In addition, the established CoMFA and CoMSIA models with reasonable statistics in the three-dimensional quantitative structure-activity relationship (3D-QSAR) study revealed the necessity of the C4-carboxyl group and other structural requirements for activity. Overall, the above results would help us to better understand the mode of action and the SAR of these derivatives, and provide crucial information for further design and development of more potent 3,4-dihydroisoquinolin-1(2H)-one derivatives as antioomycete agents against P. recalcitrans.

Antioomycete activity and mechanism of acidic electrolyzed water: a novel sanitizer to prevent saprolegniasis in grass carp

Antioomycete activity and mechanism of acidic electrolyzed water: a novel sanitizer to prevent saprolegniasis in grass carp

Hop (Humulus lupulus L.) Specialized Metabolites: Extraction, Purification, Characterization in Different Plant Parts and In Vitro Evaluation of Anti-Oomycete Activities against Phytophthora infestans

Botanicals represent a promising source of metabolites in the search for new biofungicides. In this context, this study aimed at evaluating the in vitro anti-oomycete activity of hop (Humulus lupulus L.) extracts and metabolites against Phytophthora infestans, an oomycete causing late blight disease in Solanaceae. Crude hydro-ethanolic extracts and dichloromethane sub-extracts of different parts (cones, leaves, stems and rhizomes) were characterized by UHPLC-UV–MS and some cone specialized metabolites were purified by CPC and preparative HPLC. A commercial hop cone essential oil was also analyzed by GC–MS. All extracts succeeded in inhibiting mycelial growth and spore germination with morphological alteration of the mycelium. Extracts of leaves showed a significant anti-oomycete activity compared to the extracts of cones, stems, and rhizomes. Moreover, no difference was noticed between the crude hydro-ethanolic extract and the dichloromethane sub-extract activity, except for leaves, with the apolar sub-extract being more active than the crude one. The extracts of cones succeeded in inhibiting more P. infestans than the essential oil, which appeared to be the less active evaluated modality. Some purified prenylated phenolic compounds also inhibited P. infestans although copper sulfate, a mineral fungicide control, was still more active. This study highlights the potential use of hop by-products as biofungicides to manage P. infestans.

Combinatorial Synthesis of Sulfonate Derivatives of α/β-Naphthol as Anti- Oomycete Agents.

Developing new, efficient, and environment-friendly small molecule fungicides is the key to effectively prevent and control plant pathogenic oomycetes. α/β-Naphthol is an important raw material for drug synthesis. Due to its special structure, α/β-naphthol and its analogs possess significant biological activity. The preparation and anti-oomycete activity of novel sulfonate derivatives based on α/β-naphthol against Phytophthora capsici have not been reported yet. Thirty-two sulfonate derivatives of α/β-naphthol (4a-p and 5a-p) were prepared. The structure of all title compounds was identified by 1H NMR, MS, and m.p. The anti-oomycete activity of 4a-p and 5a-p against P. capsici was determined using the mycelial growth rate method. With our ongoing research aimed at the discovery and development of fungicidal agents, 4a-p and 5a-p were designed and synthesized, and their anti-oomycete activity against P. capsici was evaluated in vitro. Two compounds 4a and 5a were found to have good anti-oomycete activity against P. capsici, and their corresponding EC50 values were 63.41 and 65.21 mg/L, respectively. It has been observed that the substituent R in these derivatives is aliphatic, which is very important for maintaining their anti-oomycete activity. The results lay a foundation for further design and development of sulfonate derivatives of α/β-naphthol as fungicidal agents. The structure- fungicidal activity relationship of α/β-naphthol derivatives is under investigation in our laboratory.