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See detailStudy of the effect of waxes on the biological activity of essential oils against Penicillium italicum Wehmer and P. digitatum Sacc, two postharvest pathogens of citrus fruits
Kouassi, Kouadio Hugues Sosthène ULg

Doctoral thesis (2012)

Control measures of postharvest fungal diseases of plants are principally based on the use of conventional chemical fungicides. However, in view of the problems associated with the use of these ones, as ... [more ▼]

Control measures of postharvest fungal diseases of plants are principally based on the use of conventional chemical fungicides. However, in view of the problems associated with the use of these ones, as well as the increasing demand for organically produced food, there is a need to replace chemical fungicides by alternative safer products, such as biological fungicides called "natural" or biofungicides. Among natural fungicides, essential oils (EOs) have been studied. EOs and their compounds present, among other things, antifungal properties and can be an interesting alternative to chemical fungicides. For this purpose, a screening of EOs according to intrinsic (yield in aromatic plant, toxicity) and extrinsic (availability, cost) criteria was carried out. Thirty EOs were selected and their inhibitory activity was tested on the in vitro growth of Penicillium italicum Wehmer, P. digitatum Sacc (pathogens of citrus fruits) and Colletotrichum musae (Berk. & M.A. Curtis) (pathogen of banana). Cinnamomum zeylanicum, C. verum and Eugenia caryophyllata proved to be the most effective at 100 ppm against the three pathogens. The biological activity of these three EOs against P. digitatum and P. italicum was evaluated on artificial infected orange fruits. EOs diluted in ethanol were able to either partially (at a concentration < 5%) or totally (at a concentration ≥ 5%) control disease incidence due to infections of both pathogens. Among the three EOs, C. zeylanicum was the most effective. In order to improve the efficiency of C. zeylanicum EO, a development of formulations consisting of this EO and Simulgel (thickening and emulsifying polymer) or waxes (shellac and / or carnauba, paraffin or polyethylene) were performed. The in vivo biological activity of the formulations was also evaluated against P. digitatum and P. italicum. In general, fungal disease control was improved in the case of fruits treated with C. zeylanicum EO supplemented with Simulgel or waxes compared to that supplemented with ethanol. The improvement was much higher with formulation consisting of C. zeylanicum-shellac (and / or carnauba) compared to the others. A SPME/GC-MS analysis of the headspace of EOs (C. zeylanicum, C. verum and E. caryophyllata) supplemented with shellac and / or carnauba (in vitro) or of oranges treated with such formulations (in vivo) highlighted the lack of some specific volatile compounds of EOs (oxygenated cyclic ones with a specific gravity superior to 0.934), in the vapor phase of the in vitro and in vivo tests, even after 7 days. While when these EOs were supplemented with ethanol, Simulgel, paraffin or polyethylene, all EO compounds were detected in the analyzed headspaces from 4 hours up to 7 days. Analysis of formulations by Fourier transform infrared spectroscopy (FTIR) revealed the formation of hydrogen bonds between such specific EO compounds and waxes (shellac and / or carnauba) This hydrogen bonds formation seems to be responsible of the non-volatilization of EO compounds and their maintaining on the fruit epidermis, thus improving citrus fruit protection. These hydrogen bonds are not observed between non-oxygenated or non-cyclic oxygenated EO compounds and none of the waxes. The present study may therefore allow a careful selection of appropriate EOs and waxes for the elaboration of effective biofungicide formulations. This application could be integrated into the packline procedure without significant modification. [less ▲]

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See detailDevelopment and application of a microplate method to evaluate the efficacy of essential oils against Penicillium italicum Wehmer, Penicillium digitatum Sacc. and Colletotrichum musea (Berk. M.A. Curtis) Arx, three postharvest fungal pathogens of fruits
Kouassi, Kouadio Hugues Sosthène ULg; Bajji, M.; Brostaux, Yves ULg et al

in Biotechnologie, Agronomie, Société et Environnement = Biotechnology, Agronomy, Society and Environment [=BASE] (2012), 16(3), 325-336

A microbioassay was developed for evaluating the in vitro antifungal activity of 30 preselected essential oils. A template based on 10 serial dilutions with eight replicates per dilution arranged on two ... [more ▼]

A microbioassay was developed for evaluating the in vitro antifungal activity of 30 preselected essential oils. A template based on 10 serial dilutions with eight replicates per dilution arranged on two 96-well ELISA plates was used as a reproducible and standardized design to identify the in vitro effectiveness of these essential oils against Penicillium italicum Wehmer, Penicillium digitatum Sacc. and Colletotrichum musea (Berk. M.A. Curtis) Arx, three postharvest fungal pathogens, on fruits. Growth of mycelium was monitored by measuring optical density (492 nm). Cinnamomum zeylanicum, Cinnamomum verum and Eugenia caryophyllus were found to be still active against all the three pathogens even at 100 ppm. Compared to other methods, this microbioassay proved to be a rapid, reproducible, and efficient method for testing the efficacy of essential oils that inhibit spore germination in P. italicum, P. digitatum and C. musea. The assay requires relatively small amounts of essential oils. [less ▲]

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See detailThe control of postharvest blue and green molds of citrus in relation with essential oil-wax formulations, adherence and viscosity.
Kouassi, Kouadio Hugues Sosthène ULg; Bajji, Mohammed; Jijakli, Haissam ULg

in Postharvest Biology & Technology (2012), 73

The use of wax coatings enriched with antifungals has significantly contributed to quality maintaining of harvested citrus fruit. On the other hand, interest in essential oils (EOs) as an alternative to ... [more ▼]

The use of wax coatings enriched with antifungals has significantly contributed to quality maintaining of harvested citrus fruit. On the other hand, interest in essential oils (EOs) as an alternative to synthetic fungicides has recently gained momentum. In this study, Cinnamomum zeylanicum EO was incorporated into a variety of commercial citrus waxes (shellac, carnauba, paraffin and polyethylene). The biological activity of these formulations against green and blue rots as well as their viscosity and adherence to the orange fruit surface were evaluated. Excellent disease control was achieved with C. zeylanicum EO incorporated in shellac and/or carnauba wax compared to other EO–wax formulations. Disease control by EO–waxes seems to depend not only on the volume that remains on the fruit skin, but also, probably on the retention of EO components on the fruit. Other factors such as formulation solubility, permeability to gases, and compatibility between EO compounds and those of waxes may also be involved in the improvement of EO efficacy. The present study may therefore allow a careful selection of ppropriate waxes for the elaboration of effective EO–wax formulations. [less ▲]

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See detailEvaluation of three essential oils as potential source of botanical fungicide
Kouassi, Kouadio Hugues Sosthène ULg; Bajji, M.; Zhiri, A. et al

Conference (2010)

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