Composition of the Essential Oil from Leaves ofAstronium graveolensJacq Grown in Colombia

Bioactivity of Selected Phenolic Acids and Hexane Extracts from Bougainvilla spectabilis and Citharexylum spinosum on the Growth of Pectobacterium carotovorum and Dickeya solani Bacteria: An Opportunity to Save the Environment

Phenolic acids and natural extracts, as ecofriendly environmental agents, can be used as bio bactericides against the growth of plant pathogenic bacteria. In this study, isolation trails from infected potato tubers and stems that showed soft rot symptoms in fields revealed two soft rot bacterial isolates and were initially identified through morphological, physiological, and pathogenicity tests. The molecular characterization of these isolates via PCR, based on the 16S rRNA region, was carried out by an analysis of the DNA sequence via BLAST and Genbank, and showed that the soft rot bacterial isolates belong to Pectobacterium carotovorum subsp. carotovorum (PCC1) and Dickeya solani (Ds1). The in vitro results of the tested phenolic acids against the cultured bacterial isolates proved that concentrations of 800, 1600, and 3200 μg/mL were the most effective. Ferulic acid was the potent suppressive phenolic acid tested against the Ds1 isolate, with an inhibition zone ranging from 6.00 to 25.75 mm at different concentrations (25–3200 μg/mL), but had no effect until reaching a concentration of 100 μg/mL in the PCC1 isolate, followed by tannic acid, which ranged from 7.00 to 25.50 mm. On the other hand, tannic acid resulted in a significant decrease in the growth rate of the PCC1 isolate with a mean of 9.11 mm. Chlorogenic acid was not as effective as the rest of the phenolic acids compared with the control. The n-hexane oily extract (HeOE) from Bougainvillea spectabilis bark showed the highest activity against PCC1 and Ds1, with inhibition zone values of 12 and 12.33 mm, respectively, at a concentration of 4000 μg/mL; while the HeOE from Citharexylum spinosum wood showed less activity. In the GC/MS analysis, nonanal, an oily liquid compound, was found ata percentage of 38.28%, followed by cis-2-nonenal (9.75%), which are the main compounds in B. spectabilis bark HeOE, and 2-undecenal (22.39%), trans-2-decenal (18.74%), and oleic acid (10.85%) were found, which are the main compounds in C. spinosum wood HeOE. In conclusion, the phenolic acids and plant HeOEs seem to raise the resistance of potato plants, improving their defense mechanisms against soft rot bacterial pathogens.

Anti-fungal activity, mechanism studies on α-Phellandrene and Nonanal against Penicillium cyclopium

BACKGROUND

Essential oils from plants have been reported to have wide spread antimicrobial activity against various bacterial and fungal pathogens, and these include α-Phellandrene, Nonanal and other volatile substances. However, biological activities of α-Phellandrene and Nonanal have been reported only in a few publications. Further investigations are necessary to determine the antimicrobial activity of these compounds, especially for individual application, to establish the possible mechanism of action of the most active compound.

RESULTS

The results are shown that α-Phellandrene and Nonanal have a dose-dependent inhibition on the mycelial growth of Penicillium cyclopium. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) are 1.7 and 1.8 mL/L for α-Phellandrene, 0.3 and 0.4 mL/L for Nonanal, respectively. The volatile compounds altered the morphology of P. cyclopium hyphae by causing loss of cytoplasmic material and distortion of the mycelia. The membrane permeability of P. cyclopium increased with increasing concentrations of the two volatile compounds, as evidenced by cell constituent release, extracellular conductivity and induced efflux of K+. Moreover, the two volatile compounds induced a decrease in pH and in the total lipid content of P. cyclopium, which suggested that cell membrane integrity had been compromised.

CONCLUSIONS

The results demonstrated that α-Phellandrene and Nonanal could significantly inhibit the mycelia growth of P. cyclopium by severely disrupting the integrity of the fungal cell membrane, leading to the leakage of cell constituents and potassium ions, and triggering an increase of the total lipid content, extracellular pH and membrane permeability. Our present study suggests that α-Phellandrene and Nonanal might be a biological fungicide for the control of P. cyclopium in postharvest tomato fruits.