Pilot testing of two biofungicide formulations for the control of citrus blue and green mold in two Moroccan packinghouses

Pichia guilliermondii strain Z1 and Bacillus subtilis strain ZH2 were previously selected for their high and reliable antagonistic activities against Penicillium digitatum (Sacc.) and blue mould (P. italicum Weh.) on citrus fruits. The effectiveness of pilot testing of wettable and a granular powder formulation based on each biocontrol agent was evaluated and compared to thiabendazole in two packinghouses. Each fruit was wounded on the outer surface on two opposite locations. Fruits intended to be treated with biofungicides were recovered just before applying the wax at packaging line. Fruits were soaked in a solution made with each formulation. Pathogenic inoculation was made 24 hours later by spraying two different varieties of fruits, Clementine ‘Nules’ and ‘Valencia-late’ orange, with a suspension of 105 conidia/ml of P. italicum or P. digitatum. The effect of treatment was evaluated after 7 days of fruit incubation at two temperatures 4 °C and 20 °C. The result showed that the control achieved with strain Z1 on ‘Valencia late’ orange was comparable to that with thiabendazole. On the other hand, the decay control was lower for all the treatments on the Clementine ‘Nules’. Nevertheless, ZH2 strain has no effect at 4 °C. Therefore, it was concluded that strain Z1 is a promising biocontrol agent for the control of major postharvest diseases of citrus in Moroccan packinghouse stations. Keywords: Citrus, biological control, formulation, packinghouse, Pichia guilliermondii, Bacillus subtili

Navigating towards decoupled aquaponic systems : a system dynamics design approach

The classical working principle of aquaponics is to provide nutrient-rich aquacultural water to a hydroponic plant culture unit, which in turn depurates the water that is returned to the aquaculture tanks. A known drawback is that a compromise away from optimal growing conditions for plants and fish must be achieved to produce both crops and fish in the same environmental conditions. The objective of this study was to develop a theoretical concept of a decoupled aquaponic system (DAPS), and predict water, nutrient (N and P), fish, sludge, and plant levels. This has been approached by developing a dynamic aquaponic system model, using inputs from data found in literature covering the fields of aquaculture, hydroponics, and sludge treatment. The outputs from the model showed the dependency of aquacultural water quality on the hydroponic evapotranspiration rate. This result can be explained by the fact that DAPS is based on one-way flows. These one-way flows results in accumulations of remineralized nutrients in the hydroponic component ensuring optimal conditions for the plants. The study also suggests to size the cultivation area based on P availability in the hydroponic component as P is an exhaustible resource and has been identified one of the main limiting factors for plant growth

Development 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

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

Production and partial characterization of chitinase from a halotolerant Planococcus rifitoensis strain M2-26

peer reviewedThis paper is the first to investigate the production and partial characterization of the chitinase enzyme from a moderately halophilic bacterium Planococcus rifitoensis strain M2-26, earlier isolated from a shallow salt lake in Tunisia. The impact of salt, salinity concentration, pH, carbon and nitrogen sources on chitinase production and activity have been determined. This is the first report on a high salt-tolerant chitinase from P. rifitoensis, since it was active at high salinity (from 5 to 30% NaCl) as well as in the absence of salt. This enzyme showed optimal activity at 70 C and retained up to 82 and 66% of its original activity at 80 or 90 C, respectively. The activity of the enzyme was also shown over a wide pH range (from 5 to 11). For characterization of the enzyme activity, the chitinase secreted in the culture supernatant was partially purified. The preliminary study of the concentrated dialysed supernatant on native PAGE showed at least three chitinases produced by strain M2-26, with highest activity approximately at 65 kDa. Thus, the thermo-tolerant and high salt-tolerant chitinases produced by P. rifitoensis strain M2-26 could be useful for application in diverse areas such as biotechnology and agro-industry

Effects of Temperature and Relative Humidity on the In Vitro and In Vivo Radial Growth of Penicillium italicum and on the Biocontrol Activity of Pichia guilliermondii, Strain Z1

peer reviewedThe objective of this study was to assess the effect of temperature (5-25°C) on the ‘in vitro’ and ‘in vivo’ growth rates of Penicillium italicum and to determine the combined effect of temperature and relative humidity (45 to 100%) on lesion size of this pathogenic fungus on Valencia late oranges, either alone or in combination with the antagonistic yeast strain Z1 of Pichia guilliermondii Wickerham. Statistical analysis showed a significant effect of temperature on the ‘in vitro’ and ‘in vivo’ radial growth of P. italicum with the maximum growth observed at temperature of 25°C. In both cases, no growth was observed at a temperature of 35°C. These factors had a significant effect on P. italicum lesion size when it was applied alone on Valencia late oranges and insignificant when yeast strain Z1 was applied 24 h before P. italicum inoculation. Our results confirm previous ‘in vitro’ findings that aw has a greater influence than temperature on P. italicum growth and highlight that the strain Z1 showed high antagonistic potential against this pathogen over a range of temperature-relative humidity regimes favouring P. italicum development