Synthesis and fungicidal activity of novel 2-(2-alkylthio-6-phenylpyrimidin-4-yl)-1H-benzimidazoles.

With the aim of exploring new benzimidazole derivative with high fungicidal activity, a series of novel 2-(2-(alkylthio)-6-phenylpyrimidin-4-yl)-1H-benzimidazoles were designed and synthesized, and their in vitro fungicidal activities were evaluated. Compounds 5a, 5f, 5g, 5h, 5i and 5l exhibited excellent fungicidal activities against Botrytis cinerea, and 5c, 5f, 5h, 5i and 5l displayed notable fungicidal activities against Sclerotinia sclerotiorum. Among them, compound 5i (R1 = fluorine, R2 = benzyl) displayed the best activity towards the two tested fungi. Docking study of 5i with ß-tubulin protein revealed that the NH moiety of benzimidazole ring generated a hydrogen bond with Gln-11 residue, and the fluorine atom of benzene ring formed a hydrogen bond with Tyr-208 residue, respectively; the benzene ring of Tyr-222 and the pyrimidine ring of 5i yielded a π-π interaction. The molecular electrostatic potential analysis elucidated the nitrogen atom of benzimidazole ring, fluorine atom of benzene ring and sulfur atom of thioether moiety were located in the negative potential regions, whereas some hydrogen atoms of benzene, benzimidazole and pyrimidine rings were located in the positive potential regions. This analysis demonstrated the reason why 5i can form hydrogen bonds with amino acid residues of target protein.

Chitosan guar nanoparticle preparation and its in vitro antimicrobial activity towards phytopathogens of rice.

The aim of the present study was to prepare chitosan guar nanoparticle (CGNP) with high antimicrobial activity to use as a bioprotectant against rice phytopathogens. Nanoparticles were prepared using sodium tripolyphosphate by the ionic gelation method. The physico-chemical properties of nanoparticles were characterized through DLS, FTIR, TEM, SEM, AFM and XRD. The application of CGNP to rice seeds stimulated seed germination and seedling growth. CGNP showed growth inhibition towards rice pathogens P. grisea and X. oryzae under in-vitro condition. Excised rice leaves treated with CGNP and challenged with P. grisea showed no blast disease symptom whereas control leaves showed very high blast disease symptom. The results of this study indicate that CGNP can be used as an antimicrobial agent to control blast, blight disease of rice.

Preparation, Characterization and Antifungal Properties of Chitosan-Silver Nanoparticles Synergize Fungicide Against Pyricularia oryzae.

Rice (Oryza sativa L.) is one of the major staple food crops of nearly two-third of the world's population. However, rice blast caused by fungus Pyricularia oryzae is generally considered the most serious disease of cultivated rice worldwide due to its extensive distribution and destructiveness under favourable climatic conditions. In this report, the combination between chitosan (CS) and silver (Ag), Ag@CS, was introduced for antifungal activity against Pyricularia oryzae extracted from blast-infected leaves. In detail, Ag@CS nanoparticles (NPs) were first synthesized and further mixed with Trihexad 700 WP (Tri), Ag@CS-Tri, against the fungus by agar diffusion method. The prepared Ag@CS-Tri NPs were characterized by Fourier transform infrared (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). In aqueous condition, Ag@CS-Tri NPs were successfully prepared and existed as spherical NPs with particle size of 17.26 ± 0.89 nm, which is an ideal size for their uptake into plant cells, indicating that the size of their parentally Ag@CS NPs is small enough to combine Tri, and their diameter is large enough to effectively penetrate the cellular membrane and kill fungi. More importantly, the antifungal property of Ag@CS-Tri NPs was significantly increased with inhibition zone around 25 nm compared with only around 12 nm of Ag@CS at the same concentration of Ag (2 ppm) and CS (4000 ppm). These results demonstrated that the synergistic effect of Tri and Ag@CS NPs can be a potential candidate with high antifungal activity for the use of antibiotics in agriculture.

Application of Copper-Chitosan Nanoparticles Stimulate Growth and Induce Resistance in Finger Millet (Eleusine coracana Gaertn.) Plants against Blast Disease.

Copper-chitosan nanoparticle (CuChNp) was synthesized and used to study its effect on finger millet plant as a model plant system. Our objective was to explore the efficacy of CuChNp application to control blast disease of finger millet. CuChNp was applied to finger millet either as a foliar spray or as a combined application (involving seed coat and foliar spray). Both the application methods enhanced growth profile of finger millet plants and increased yield. The increased yield was nearly 89% in combined application method. Treated finger millet plants challenged with Pyricularia grisea showed suppression of blast disease development when compared to control. Nearly 75% protection was observed in the combined application of CuChNp to finger millet plants. In CuChNp treated finger millet plants, a significant increase in defense enzymes was observed, which was detected both qualitatively and quantitatively. The suppression of blast disease correlates well with increased defense enzymes in CuChNp treated finger millet plants.

Bioactivity and structure-activity relationship of cinnamic acid esters and their derivatives as potential antifungal agents for plant protection.

A series of cinnamic acid esters and their derivatives were synthesized and evaluated for antifungal activities in vitro against four plant pathogenic fungi by using the mycelium growth rate method. Structure-activity relationship was derived also. Almost all of the compounds showed some inhibition activity on each of the fungi at 0.5 mM. Eight compounds showed the higher average activity with average EC50 values of 17.4-28.6 µg/mL for the fungi than kresoxim-methyl, a commercial fungicide standard, and ten compounds were much more active than commercial fungicide standards carbendazim against P. grisea or kresoxim-methyl against both P. grisea and Valsa mali. Compounds C1 and C2 showed the higher activity with average EC50 values of 17.4 and 18.5 µg/mL and great potential for development of new plant antifungal agents. The structure-activity relationship analysis showed that both the substitution pattern of the phenyl ring and the alkyl group in the alcohol moiety significantly influences the activity. There exists complexly comprehensive effect between the substituents on the phenyl ring and the alkyl group in the alcohol moiety on the activity. Thus, cinnamic acid esters showed great potential the development of new antifungal agents for plant protection due to high activity, natural compounds or natural compound framework, simple structure, easy preparation, low-cost and environmentally friendly.

Design, synthesis and fungicidal activity of novel 2-substituted aminocycloalkylsulfonamides.

A series of novel 2-substituted aminocycloalkylsulfonamides were designed and synthesized by highly selective N-alkylation reaction, whose structures were characterized by 1H NMR, 13C NMR and HRMS. Among them, the configuration of compounds III12 and III20 were confirmed by X-ray single crystal diffraction. Bioassays demonstrated that the title compounds had considerable effects on different strains of Botrytis cinerea and Pyricularia grisea. Comparing with positive control procymidone (EC50=10.31mg/L), compounds III28, III29, III30 and III31 showed excellent fungicidal activity against a strain of B. cinerea (CY-09), with EC50 values of 3.17, 3.04, 2.54 and 1.99mg/L respectively. Their in vivo fungicidal activities were also better than the positive controls cyprodinil, procymidone, boscalid and carbendazim in pot experiments. Moreover, the fungicidal activity of III28 (EC50=4.62mg/L) against P. grisea was also better than that of the positive control isoprothiolane (EC50=6.11mg/L). Compound III28 would be great promise as a hit compound for further study based on the structure-activity relationship.

Chitosan nanoparticle induced defense responses in fingermillet plants against blast disease caused by Pyricularia grisea (Cke.) Sacc.

The in vitro antifungal properties of chitosan nanoparticle and its role in protection of fingermillet plants from blast disease were evaluated. Chitosan nanoparticle inhibited the radial growth of Pyricularia grisea indicating the antifungal property. Application of chitosan nanoparticle delayed blast symptom expression on fingermillet leaves for 25days while it was on 15day in control plants. Chitosan naoparticle was able to induce the reactive oxygen species and the level of peroxidase actvitiy in leaves of fingermillet, which might be the reason for delayed symptom. The treated plants showed reduced disease incidence when compared to untreated control plants. These results suggested the role of chitosan nanoparticle in protecting fingermillet plants from P. grisea infection.

Biological preparation of chitosan nanoparticles and its in vitro antifungal efficacy against some phytopathogenic fungi.

The aim of the present study was to prepare Chitosan nanoparticles through biological method with high antifungal activities. Chitosan nanoparticles were prepared by the addition of anionic proteins isolated from Penicillium oxalicum culture to chitosan solutions. The formation of chitosan nanoparticles was preliminary confirmed by UV-vis spectrophotometric analysis. The physico-chemical properties of the chitosan nanoparticles were determined by size and zeta potential analysis, FTIR analysis, HRTEM and XRD pattern. The chitosan nanoparticles were evaluated for its potential to inhibit the growth of phytopathogens viz., Pyricularia grisea, Alternaria solani, Fusarium oxysporum. It is evident from our results that chitosan nanoparticles inhibit the growth of phytopathogens tested. Chitosan nanoparticle treated chickpea seeds showed positive morphological effects such as enhanced germination%, seed vigor index and vegetative biomass of seedlings. All these results indicate that chitosan nanoparticle can be used further under field condition to protect various crops from the devastating fungal pathogens as well as growth promoters.

Preparation of Chitosan nanoparticles and its effect on detached rice leaves infected with Pyricularia grisea.

The aim of the present study was to prepare chitosan nanoparticles to evaluate their effect on protection of rice plants from blast fungus. Nanoparticles were prepared using the ionic gelation method by the interaction of Chitosan and sodium tripolyphosphate. The particle size, polydispersity index, zetapotential and structure was confirmed by DLS, FTIR, TEM and XRD. The Chitosan nanoparticle was evaluated for suppression of rice blast fungus (Pyricularia grisea) under the detached leaf condition. It is evident from our results that chitosan nanoparticle have potential in suppressing blast disease of rice which can be used further under field condition to protect rice plants from the devastating fungus.

Antifungal activities of some indole derivatives.

Nine indole derivatives were evaluated in vitro against Fusarium graminearum, Alternaria alternata, Helminthosporium sorokinianum, Pyricularia oryzae, Fusarium oxysporum f. sp. vasinfectum, Fusarium oxysporum f. sp. cucumarinum, and Alternaria brassicae. Most of the compounds were found to possess antifungal activities. Especially compounds 2, 5, 8, and 9 exhibited broad-spectrum antifungal activities against the above-mentioned seven phytopathogenic fungi, and showed more potent activities than hymexazole, a commercial agricultural fungicide.