Evaluating the Antifungal Potential of Botanical Compounds to Control Botryotinia fuckeliana and Rhizoctonia solani

Inhibitory Activity Against Rhizoctonia Solani and Chemical Composition of Extract from Moutan Cortex

Rice sheath blight (RSB), caused by Rhizoctonia solani, is a significant disease of rice. The negative effects of chemical fungicides have created an urgent need for low-toxicity botanical fungicides. Our previous research revealed that the ethanol crude extract of Moutan Cortex (MC) exhibited superior antifungal activity against R. solani at 1000 μg/mL, resulting in a 100 % inhibition rate. The antifungal properties were mainly found in the petroleum ether extract. However, the active ingredients of the extract are still unclear. In this study, gas chromatography-mass spectrometry (GC-MS) was utilised for the analysis of its chemical components. The mycelium growth rate method was utilized to detect the antifungal activity. The findings indicated that paeonol constituted the primary active component, with a content of more than 96 %. Meanwhile, paeonol was the most significant antifungal active ingredient, the antifungal activity of paeonol (EC50=44.83 μg/mL) was much higher than that of β-sitosterol and ethyl propionate against R. solani. Observation under an optical microscope revealed that paeonol resulted in abnormal mycelial morphology. This study provided theoretical support for identifying monomer antifungal compounds and developing biological fungicides for R. solani.

Biocontrol Activity of Aromatic and Medicinal Plants and Their Bioactive Components against Soil-Borne Pathogens

Soil-borne phytopathogens can have detrimental effects on both cereal and horticultural crops resulting in serious losses worldwide. Due to their high efficiency and easy applicability, synthetic pesticides are still the primary choice in modern plant disease control systems, but stringent regulations and increasing environmental concerns make the search for sustainable alternatives more pressing than ever. In addition to the incorporation of botanicals into agricultural practices, the diversification of cropping systems with aromatic and medicinal plants is also an effective tool to control plant diseases through providing nutrients and shaping soil microbial communities. However, these techniques are not universally accepted and may negatively affect soil fertility if their application is not thoroughly controlled. Because the biocontrol potential of aromatic and medicinal plants has been extensively examined over the past decades, the present study aims to overview the recent literature concerning the biopesticide effect of secondary metabolites derived from aromatic and medicinal plants on important soil-borne plant pathogens including bacteria, fungi, and nematodes. Most of the investigated herbs belong to the family of Lamiaceae (e.g., Origanum spp., Salvia spp., Thymus spp., Mentha spp., etc.) and have been associated with potent antimicrobial activity, primarily due to their chemical constituents. The most frequently tested organisms include fungi, such as Rhizoctonia spp., Fusarium spp., and Phytophthora spp., which may be highly persistent in soil. Despite the intense research efforts dedicated to the development of plant-based pesticides, only a few species of aromatic herbs are utilized for the production of commercial formulations due to inconsistent efficiency, lack of field verification, costs, and prolonged authorization requirements. However, recycling the wastes from aromatic and medicinal plant-utilizing industries may offer an economically feasible way to improve soil health and reduce environmental burdens at the same time. Overall, this review provides comprehensive knowledge on the efficiency of aromatic herb-based plant protection techniques, and it also highlights the importance of exploiting the residues generated by aromatic plant-utilizing sectors as part of agro-industrial processes.

The Citrus reticulata essential oil: evaluation of antifungal activity against penicillium species related to bakery products spoilage

Fungal food spoilage plays a key role in the deterioration of food products, and finding a suitable natural preservative can solve this problem. Therefore, antifungal activity of green mandarin (Citrus reticulata) essential oil (GMEO) in the vapor phase against the growth of Penicillium (P.) expansum and P. chrysogenum inoculated on wheat bread (in situ experiment) was investigated in the current research. The volatile compounds of the GMEO were analyzed by a gas chromatograph coupled to a mass spectrometer (GC–MS), and its antioxidant activity was determined by testing free radical-scavenging capacity (DPPH assay). Moreover, the disc diffusion method was used to analyze the antifungal activity of GMEO in in vitro conditions. The results demonstrate that the Citrus reticulata EO consisted of α-limonene as the most abundant component (71.5%), followed by γ-terpinene (13.9%), and β-pinene (3.5%), and it displayed the weak antioxidant activity with the value of inhibition 5.6 ±0.7%, which corresponds to 103.0 ±6.4 µg TEAC.mL-1. The findings from the GMEO antifungal activity determination revealed that values for the inhibition zone with disc diffusion method ranged from 0.00 ±0.00 (no antifungal effectiveness) to 5.67 ±0.58 mm (moderate antifungal activity). Finally, exposure of Penicillium strains growing on bread to GMEO in vapor phase led to the finding that 250 μL.L-1 of GMEO exhibited the lowest value for mycelial growth inhibition (MGI) of P. expansum (-51.37 ±3.01%) whose negative value reflects even supportive effect of the EO on the microscopic fungus growth. On the other hand, GMEO at this concentration (250 μL.L-1) resulted in the strongest inhibitory action (MGI: 54.15 ±1.15%) against growth of P. chrysogenum. Based on the findings it can be concluded that GMEO in the vapor phase is not an effective antifungal agent against the growth of P. expansum inoculated on bread; however, its antifungal potential manifested against P. chrysogenum suggests GMEO to be an appropriate alternative to the use of chemical inhibitors for bread preservation.

In Vitro Antimicrobial Activity of Lavender, Mint, and Rosemary Essential Oils and the Effect of Their Vapours on Growth of Penicillium spp. in a Bread Model System

The chemical composition, antioxidant activity, and antimicrobial properties of three commercially available essential oils: rosemary (REO), lavender (LEO), and mint (MEO), were determined in the current study. Our data revealed that the major components of REO, MEO, and LEO were 1,8-cineole (40.4%), menthol (40.1%), and linalool acetate (35.0%), respectively. The highest DPPH radical-scavenging activity was identified in MEO (36.85 ± 0.49%) among the investigated EOs. Regarding antimicrobial activities, we found that LEO had the strongest inhibitory efficiencies against the growth of Pseudomonas aeruginosa and Candida (C.) tropicalis, MEO against Salmonella (S.) enterica, and REO against Staphylococcus (S.) aureus. The strongest antifungal activity was displayed by mint EO, which totally inhibited the growth of Penicillium (P.) expansum and P. crustosum in all concentrations; the growth of P. citrinum was completely suppressed only by the lowest MEO concentration. The lowest minimal inhibitory concentrations (MICs) against S. enterica, S. aureus, and C. krusei were assessed for MEO. In situ analysis on the bread model showed that 125 µL/L of REO exhibited the lowest mycelial growth inhibition (MGI) of P. citrinum, and 500 µL/L of MEO caused the highest MGI of P. crustosum. Our results allow us to make conclusion that the analysed EOs have promising potential for use as innovative agents in the storage of bakery products in order to extend their shelf-life.