Plants-derived bioactives: Novel utilization as antimicrobial, antioxidant and phytoreducing agents for the biosynthesis of metallic nanoparticles.

Medicinal and aromatic higher plants are sustainable resources for natural product compounds, including essential oils, phenolics, flavonoids, alkaloids, glycosides, and saponins. Extractives and essential oils as well as their bioactive compounds have many uses due to their antimicrobial, anticancer, and antioxidant properties as well as application in food preservation. These natural compounds have been reported in many works, for instance biofungicide with phenolic and flavonoid compounds being effective against mold that causes discoloration of wood. Additionally, the natural extracts from higher plants can be used to mediate the synthesis of nanoparticle materials. Therefore, in this review, we aim to promote and declare the use of natural products as environmentally eco-friendly bio-agents against certain pathogenic microbes and make recommendations to overcome the extensive uses of conventional pesticides and other preservatives.

Foliar Application of Bio-Stimulants Enhancing the Production and the Toxicity of Origanum majorana Essential Oils Against Four Rice Seed-Borne Fungi.

In the present study, the enhancement of the production of Origanum majorana essential oils (EOs) was studied by treating plants with ascorbic acid (AA) and tryptophan (Trp) at concentrations of 100, 200 and 300 mg/L and Moringa oleifera leaf extract (MLE) at 2.5%, 5% and 10% as foliar applications during the seasons 2018-2019. The toxicities of the EOs were assayed against four seed-borne fungi (Bipolaris orzyae, Curvularia lunata, Fusarium verticilliodies and F. graminearum) isolated from rice grains (Oryzae sativa). Vegetative growth parameters and EO production were enhanced by the application of AA, Trp and MLE in both seasons. Analysis of the EOs by Gas chromatography-mass spectrometry (GC-MS) showed that the main chemical constituents were terpineol (cis-ß-(1-terpinenol)), terpinen-4-ol, 4-thujanol (sabinene hydrate), α-terpineol, cymene and sabinene. The highest fungal mycelial growth inhibition (FMGI) percentages against F. verticilliodies were 94.57% and 92.63% as MLE at 5% and 10%, respectively, was applied to plants and 85.60% and 82.19% against F. graminearum as Trp was applied to plants at 300 and 200 mg/L, respectively. EOs from the treated plant with MLE (10%) observed the highest FMGI (84.46%) against B. oryzae, and EOs from plants treated with AA as foliar application at 300 and 200 mg/L showed the highest FMGI values of 81.11% and 81.85%, respectively, against the growth of C. lunata. Application of EOs extracted from plants treated with Trp, AA and MLE at 300 mg/L, 300 mg/L and 10%, respectively, or untreated plants to rice seeds inhibited or decreased the fungal infection percentage from 82.5% (naturally infected grains) to 1.75%, 10.5%, 17.5% and 18.5%, respectively. In conclusion, the extracted EOs affected by the foliar application of O. majorana plants with Trp, AA, and MLE could be useful as a biofungicide against rice seed-borne fungi.

Toxicity effects of Eriocephalus africanus L. leaf essential oil against some molecularly identified phytopathogenic bacterial strains.

Essential oil (EO) from Eriocephalus africanus L. leaves was evaluated against the growth of some phytopathogenic bacteria including Agrobacerium tumifaciens, Dickeya solani, Erwinia amylovora, Pseudomonas cichorii and Serratia pulmithica using the disc diffusion method and minimum inhibitory concentration (MIC) evaluation. Ten compounds in the EO with dominance of Artemisia ketone (2,5,5-trimethyl-2,6-heptadien-4-one) (77.92%) and ledol (19.92%) were revealed. The antibacterial activity indicated efficacy of essential oil against majority of strains isolated. The most effective action was recorded against D. solani, by 7.5 and 10 µL of oil, with 18.33 mm and 100 µg/mL as zone inhibition and MIC, respectively, whereas the lowest activity was exhibited against P. cichorii (diameter inhibition = 6.66 mm at 10 µL of oil, MIC = 100 µg/mL). The strain S. pulmithica appears to be resistant to the oil when the activity is measured by 10 µL of oil but its growth inhibition was reported with a MIC of 100 µg/mL.

Antibacterial activity of the bioactive compounds identified in three woody plants against some pathogenic bacteria.

Three bacterial isolates were identified from infected potato tubers showing soft and blackleg like symptoms as well as one isolate from infected pear tree showing crown gall symptom. Conventional and molecular identification proved that bacterial isolates belonging to Pectobacterium carotovorum subsp. carotovorum, Pectobacterium atrosepticum, Dickeya solani and Agrobacterium tumefaciens. The above plant bacterial isolates and human pathogenic bacteria Escherichia coli, Sarcina lutea, and Staphylococcus aureus were used for the bioassay. The chloroform leaf extracts from Duranta plumieri variegata, Lantana camara, and Citharexylum spinosum were assayed for their antibacterial activity by measuring the inhibition zones and minimum inhibitory concentrations (MICs). The suggested chemical compositions of extracts were analyzed using GC/MS apparatus. The main compounds in leaf extract of L. camara were 5,8-diethyl-dodecane, pyrimidin-2-one, 4-[N-methylureido]-1-[4-methylaminocarbonyloxymethyl, oleic acid,3-(octadecyloxy)propyl ester; in D. plumieri were 4,7-dimethoxy-2-methylindan-1-one and 5-(hexadecyloxy)-2-pentadecyl-,trans-1,3-dioxane; and in C. spinosum were N-[5-(3-hydroxy-2-methylpropenyl)-1,3,4,5-tetrahydrobenzo[cd]indol-3-yl]-N-methylacetamide. Promising activity was found against A. tumefaciens, E. coli, P. carotovorum, Sar. lutea, and Staph. aureus with MIC values of 8, 128, 64, 500 and 500 µg/mL, respectively, as L. camara leaf extract was applied. D. plumieri leaf extract showed good activity against D. solani and P. atrosepticum with MIC values of 16 µg/mL and 128 µg/mL, respectively. On the other hand, weak bioactivity was found with leaf extract from C. spinosum. It could be concluded that leaf extracts from D. plumieri and L. camara have a promising antibacterial agents.

Antibacterial activities of the phytochemicals-characterized extracts of Callistemon viminalis, Eucalyptus camaldulensis and Conyza dioscoridis against the growth of some phytopathogenic bacteria.

Three bacterial isolates were isolated from infected potato tubers showing soft and brown rots like symptoms as well as one isolate from infected peach tree showing crown gall symptom. The morphological, biochemical and molecular assays proved that bacterial isolates belonging to Pectobacterium carotovorum subsp. carotovorum, Ralstonia solanacearum, Dickeya spp. and Agrobacterium tumefaciens. The acetone (AcE) and n-butanol (ButE) extracts of Callistemon viminalis flowers and essential oil from aerial parts of Conyza dioscoridis as well as ButE of Eucalyptus camaldulensis bark are evaluated at different concentrations against the growth of the isolated bacteria. The diameter of inhibition zone (IZ) and the minimum inhibitory concentrations (MICs) are compared. Results indicated that the highest IZ values were 20.0 mm and 18.3 mm for E. camaldulensis bark ButE and C. viminalis flower ButE, respectively, against P. carotovorum; 16.3 mm and 16.0 mm for E. camaldulensis bark ButE and C. viminalis flower ButE, respectively, against R. solanacearum; 18.5 mm for C. viminalis flower AcE and C. dioscoridis aerial parts EO against Dickeya spp.; and 15.0 mm for C. viminalis flower AcE against A. tumefaciens. MICs ranged from <16 µg/mL for D. solani to >4000 µg/mL for A. tumefaciens. It was proved that C. viminalis flowers AcE contains mainly 5-hydroxymethylfurfural (20.6%), palmitic acid (18.5%), and pyrogallol (16.4%); while C. viminalis flower ButE contains palmitic acid (36.3%), 2-hydroxymyristic acid (9.4%), 5-hydroxymethylfurfural (7.2%), and shikimic acid (6.6%); whereas E. camaldulensis bark ButE contains 8-nonynoic acid methyl ester (45.6), camphor (30.9%), menthol (8.8%), and 1,8-cineole (eucalyptol) (8.2%), whilst the EO of C. dioscoridis aerial parts comprises Z-(13,14-epoxy)tetradec-11-en-1-ol acetate (11.6%), γ-elemene (10.2%), tau.-muurolol (7.1%), and cadina-3,9-diene (4.7%). It can be concluded that phytochemical extracts of C. viminalis, E. camaldulensis and C. dioscoridis demonstrated strong to moderate antibacterial effects against the studied plant bacterial pathogens.

Medicinal and biological values of Callistemon viminalis extracts: History, current situation and prospects.

Callistemon viminalis (C. viminalis) is a plant that has been reported to have various medicinal values such as antibacterial, antifungal, antioxidant activities and other pharmaceutical and insecticidal properties. This review covers the potentials, applications and properties of different extracts from different parts (branches, flowers, fruits, bark, leaves) of C. viminalis. Furthermore, the chemical structures of the bioactive compounds were reported for biological activities. All the results supported the traditional uses of C. viminalis in folk medicine. In addition, some researches supported the use of C. viminalis extracts for the preparation of metal oxide nanoparticles.