Synthesis, Antifungal Activity, 3D-QSAR, and Molecular Docking Study of Novel Menthol-Derived 1,2,4-Triazole-Thioether Compounds

A series of novel menthol derivatives containing 1,2,4-triazole-thioether moiety were designed, synthesized, characterized structurally, and evaluated biologically to explore more potent natural product-based antifungal agents. The bioassay results revealed that at 50 μg/mL, some of the target compounds exhibited good inhibitory activity against the tested fungi, especially against Physalospora piricola. Compounds 5b (R = o-CH3 Ph), 5i (R = o-Cl Ph), 5v (R = m, p-OCH3 Ph) and 5x (R = α-furyl) had inhibition rates of 93.3%, 79.4%, and 79.4%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Compounds 5v (R = m, p-OCH3 Ph) and 5g (R = o-Cl Ph) held inhibition rates of 82.4% and 86.5% against Cercospora arachidicola and Gibberella zeae, respectively, much better than that of the commercial fungicide chlorothalonil. Compound 5b (R = o-CH3 Ph) displayed antifungal activity of 90.5% and 83.8%, respectively, against Colleterichum orbicalare and Fusarium oxysporum f. sp. cucumerinum. Compounds 5m (R = o-I Ph) had inhibition rates of 88.6%, 80.0%, and 88.0%, respectively, against F.oxysporum f. sp. cucumerinu, Bipolaris maydis and C. orbiculare. Furthermore, compound 5b (R = o-CH3 Ph) showed the best and broad-spectrum antifungal activity against all the tested fungi. To design more effective antifungal compounds against P. piricola, 3D-QSAR analysis was performed using the CoMFA method, and a reasonable 3D-QSAR model (r2 = 0.991, q2= 0.514) was established. The simulative binding pattern of the target compounds with cytochrome P450 14α-sterol demethylase (CYP51) was investigated by molecular docking.

Presence and correlation of Fusarium graminearum and deoxynivalenol accumulation in silage corn plant parts

Corn silage, made from Zea mays, is a high energy feed that is important for feeding dairy cows. Plant diseases, such as those caused by Fusarium graminearum , can decrease silage corn yields and quality. Fusarium graminearum (teleomorph Gibberella zeae) is an ascomycete fungus that causes Gibberella ear and stalk rot in corn. Fusarium graminearum produces deoxynivalenol (DON), a secondary metabolite toxic to humans and animals. An understanding of the distribution of DON and F. graminearum throughout the corn plant is important for determining the quality of corn silage. A partitioned sample experiment that included two brown-midrib silage hybrids and three fungicide treatments was conducted in research plots located in Arlington, Wisconsin in 2018 and 2019. At harvest, stalk and ear parts were physically separated, dried, and ground for analysis. DON concentration (ppm) was determined using ELISA and F. graminearum DNA concentration (pg/ng) was determined using qPCR. Both DON and F. graminearum DNA were detected in all samples, demonstrating accumulation of the fungus in both stalks and ears of the plant. In 2018, DON contamination was as high as 30 ppm and varied drastically between stalks and ears. In 2019, DON concentrations were much lower (<5ppm), but were consistently higher in stalk samples than ear samples. Across all samples DON concentrations and F. graminearum accumulation were highly correlated within the separated stalk (r=0.78) and ear portions (r=0.87) but were not correlated between ears and stalks. Depending on the weather and planting conditions in a given year, either stalk infections or ear infections may occur by F. graminearum leading to subsequent DON increases in those respective parts that are independent of each other.

Novel Thiochromanone Derivatives Containing a Sulfonyl Hydrazone Moiety: Design, Synthesis, and Bioactivity Evaluation

A series of novel thiochromanone derivatives containing a sulfonyl hydrazone moiety were designed and synthesized. Their structures were determined by 1H-NMR, 13C-NMR, and HRMS. Bioassay results showed that most of the target compounds revealed moderate to good antibacterial activities against Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicolaby, and Xanthomonas axonopodis pv. citri. Compound 4i had the best inhibitory activity against Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicolaby, and Xanthomonas axonopodis pv. citri, with the EC50 values of 8.67, 12.65, and 10.62 μg/mL, which were superior to those of Bismerthiazol and Thiodiazole-copper. Meanwhile, bioassay results showed that all of the target compounds proved to have lower antifungal activities against Sclerotinia sclerotiorum, Fusarium oxysporum, Gibberella zeae, Rhizoctonia solani, Verticillium dahlia, and Botrytis cinerea than those of Carbendazim.

Synthesis, Antifungal Activity, and 3D-QSAR Study of Novel Nopol-Derived 1,3,4-Thiadiazole-Thiourea Compounds

A series of novel nopol derivatives bearing the 1,3,4-thiadiazole-thiourea moiety were designed and synthesized by multi-step reactions in search of potent natural product-based antifungal agents. Their structures were confirmed by FT-IR, NMR, ESI-MS, and elemental analysis. Antifungal activity of the target compounds was preliminarily evaluated by in vitro methods against Fusarium oxysporum f. sp. cucumerinum, Cercospora arachidicola, Physalospora piricola, Alternaria solani, Gibberella zeae, Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. All the target compounds exhibited better antifungal activity against P. piricola, C. arachidicola, and A. solani. Compound 6j (R = m, p-Cl Ph) showed the best broad-spectrum antifungal activity against all the tested fungi. Compounds 6c (R = m-Me Ph), 6q (R = i-Pr), and 6i (R = p-Cl Ph) had inhibition rates of 86.1%, 86.1%, and 80.2%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Moreover, compounds 6h (R = m-Cl Ph) and 6n (R = o-CF3 Ph) held inhibition rates of 80.6% and 79.0% against C. arachidicola and G. zeae, respectively, much better than that of the commercial fungicide chlorothalonil. In order to design more effective antifungal compounds against A. solani, analysis of the three-dimensional quantitative structure–activity relationship (3D-QSAR) was carried out using the CoMFA method, and a reasonable and effective 3D-QSAR model (r2 = 0.992, q2 = 0.753) has been established. Furthermore, some intriguing structure–activity relationships were found and are discussed by theoretical calculation.

Novel Fluorinated 7-Hydroxycoumarin Derivatives Containing an Oxime Ether Moiety: Design, Synthesis, Crystal Structure and Biological Evaluation

A series of fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety have been designed, synthesized and evaluated for their antifungal activity. All the target compounds were determined by 1H-NMR, 13C-NMR, FTIR and HR-MS spectra. The single-crystal structures of compounds 4e, 4h, 5h and 6c were further confirmed using X-ray diffraction. The antifungal activities against Botrytis cinerea (B. cinerea), Alternariasolani (A. solani), Gibberella zeae (G. zeae), Rhizoctorzia solani (R. solani), Colletotrichum orbiculare (C. orbiculare) and Alternaria alternata (A. alternata) were evaluated in vitro. The preliminary bioassays showed that some of the designed compounds displayed the promising antifungal activities against the above tested fungi. Strikingly, the target compounds 5f and 6h exhibited outstanding antifungal activity against B. cinerea at 100 μg/mL, with the corresponding inhibition rates reached 90.1 and 85.0%, which were better than the positive control Osthole (83.6%) and Azoxystrobin (46.5%). The compound 5f was identified as the promising fungicide candidate against B. cinerea with the EC50 values of 5.75 μg/mL, which was obviously better than Osthole (33.20 μg/mL) and Azoxystrobin (64.95 μg/mL). Meanwhile, the compound 5f showed remarkable antifungal activities against R. solani with the EC50 values of 28.96 μg/mL, which was better than Osthole (67.18 μg/mL) and equivalent to Azoxystrobin (21.34 μg/mL). The results provide a significant foundation for the search of novel fluorinated 7-hydroxycoumarin derivatives with good antifungal activity.

Progress in the management of Fusarium head blight of wheat: An overview

Fusarium head blight (FHB), also known as head scab, is a devastating fungal disease that affects small grain cereal crops such as wheat (Triticum aestivum L.). The predominant causal agent, Fusarium graminearum Schwabe (teleomorph: Gibberella zeae (Schwein.) Petch), is ranked the fourth most important fungal plant pathogen worldwide. Apart from yield and quality losses, mycotoxin production can occur from FHB infection, resulting in harmful effects on human and animal health. Some level of disease control may be achieved by using certain fungicides and agronomic practices plus host resistance. In South Africa, there are currently no registered fungicides or bio-fungicides, no resistant wheat cultivars and only limited control is achieved by cultural practices. Because effective disease reduction cannot be achieved by using a single strategy, the integration of multiple management strategies can enhance disease control. We review possible strategies for reducing the risk for FHB infections that are relevant to the context of South Africa and other wheat growing areas in Africa.

Bioecological features of pathogenic mycobiota formation in flower and decorative plants (on the example of Callistephus chinensis (L.) Nees) urban ecosystems greenization

The phytopathological condition of Chinese calisthephus groups in urbanized ecosystems of the forest-steppe zone was assessed and the species composition of pathogenic mycobiota was established as the main natural causes of violations of the complex green zone and compositional integrity of flower crops phyto-cenoses. The species composition was specified and a taxonomic assessment of the pathocomplex was carried out, where the kingdom of Fungi occupies a dominant place and is represented by 20 (84 %) species of pathogens from 11 (85 %) genera, 9 (82 %) families, 7 (78 %) orders, 2 (67 %) divisions, where Ascomycota has an advantage, which is represented by 18 (90 %) species, and the number of species is dominated by the orders Dothideales (6 species, 26 %) and Hypocreales (5 species, 21.7 %). Ecological niches of the main pathogens of Chinese calisthephus were established: micromycetes Botryotinia fuckeliana (de Bary) Whetzel., Fusarium oxysporum Schltdl. (1824), Verticillium albo-atrum Reinke & Berthold. V.dahliae Kleb. detected on all vegetative and reproductive organs; Phytophthora cactorum J. Schröt. (1886) – underground and aboveground; Rhizoctonia solani J.G. Kühn (1858) – underground parts and seeds, Alternaria zinniae M.B. Ellis (1972) – aboveground parts and seeds. In the phytopathogenic complex of underground organs the dominant place is fusarium root rot caused by Fusarium oxysporum, F.culmorum (Wm.G. Sm.) Sacc. (1895), Gibberella zeae (Schwein.) Petch, G. avenacea R.J. Cooke, Haematonectria haematococca (Berk. & Broome) Samuels & Rossman with average annual prevalence ranging from 5 to 89 %. The average annual prevalence of fusarium wilt of Chinese calistefus caused by Fusarium oxysporum, F. oxysporum f. callistephi W.C. Snyder & H.N. Hansen was 40.9 %. Pathogenic mycobiota according to the indicators of infection transmission factor belongs to the following ecological groups: airborne infection (54.2 %), soil infection (45.8 %); according to ecological and trophic properties they can be classified as biotrophs (70.8 %) and saprotrophs (29.2 %). Key words: urban ecosystem, flower-ornamental plants, mycobiota, phytopathogenic complex, Callistephus chinensis (L.) Nees, Fusarium oxysporum Schlecht., Ecological groups.

Antimicrobial Activity of Chrysoeriol 7 and Chochlioquinone 9, White-Backed Planthopper-Resistant Compounds, Against Rice Pathogenic Strains

As environmental damage caused by chemical pesticides appears worldwide, eco-friendly agriculture is increasing, and finding eco-friendly pesticide materials has become very important. Chrysoeriol and cochlioquinone, two flavonoids, act as an antibacterial and antioxidant, and increase the resistance of rice to the white-backed planthopper (WBPH). In this experiment, chrysoeriol 7 (C7) and cochlioquinone 9 (C9) were extracted from rice inoculated with the WBPH using MeOH, and cultivars with high extraction efficiency were selected. In addition, the antimicrobial activity of C7 and C9 against various pathogens causing disease in rice was tested. The results show that C7 has antifungal activity against Fusarium graminearum and Pythium graminicola, and C9 show antifungal activity against Cladosporium herbarum, Cladosporium cladosporioides, Gibberella zeae, Fusarium graminearum and Pythium graminicola. When both substances were treated at a concentration of 1000 ppm, they showed high inhibition rates of 62.3% and 36.2% against P.graminicola, respectively. After that, a phylogenetic tree was created to clarify the relationship between the microorganisms whose growth was inhibited and divided into three groups. This result can contribute to the study of biopesticide materials that can control pests and pathogens.

Influence of pH on the Dehydrogenase Activity in Fusarium graminearum Species Schwb. Telemorph Gibberella Zeae (Schwb.) Petsch) Production of Mycotoxins

Dehydrogenases are enzymes that catalyzes the electron transfer reactions and act according to their redox potential (rH) from negative rH values to the highest positive ones. Depending on the chemical nature of the substrate which donates hydrogen, dehydrogenase bear appropriate names: α-ketoglutarate glucoso 6-fosfat dehidrogenase, isocitrate dehydrogenase, malate dehydrogenase, etc. The paper presents the influence of pH against the dehydrogenase activity, both if the mycelium and culture liquid, at 21 and 28 days from the inoculation.