In the province of South Kivu (Democratic Republic of Congo), warm and humid climatic conditions favor the development and spreading of phytopathogens. The resulting diseases cause important losses in production both in crop and after harvest. In this study, we wanted to evaluate the potential of Bacillus amyloliquefaciens as biocontrol agent to fight some newly isolated endemic fungal pathogens infesting maize. The strain S499 has been selected based on its high in vitro antagonistic activity correlating with a huge potential to secrete fungitoxic lipopeptides upon feeding on maize root exudates. Biocontrol activity of S499 was further tested on infected plantlets in growth chamber and on plants grown under field conditions over an entire cropping period. We observed a strong protective effect of this strain evaluated at two different locations with specific agro-ecological conditions. Interestingly, disease protection was associated with higher yields and our data strongly suggest that, in addition to directly inhibit pathogens, the strain may also act as biofertilizer through the solubilization of phosphorus and/or by producing plant growth hormones in the rhizosphere. This work supports the hope of exploiting such technologically advantageous bacilli for the sake of sustainable local production of this important crop in central Africa.
Objective: In the highlands of South-Kivu province of DR Congo, cassava is grown on marginal land not suitable for other crops. Walungu territory for instance is dominated by acidic soils and has the highest nutrient depletion rate in the country. On such types of soil, nutrient depletion is accompanied by a decrease in the availability of phosphorus and many other nutrients. The use of Arbuscular mycorrhizal fungi (AMF) would therefore be an alternative to improve the phosphate nutrition of cassava under different soil conditions.
Methodology and results: The experiment reported in the current study was conducted in pots under semi-controlled conditions. Ferrallitic soil from Walungu was used. Soil was sterilized or not and then inoculated with the AMF Rhizophagus irregularis (RI) strain. Results showed that inoculation with an exotic AMF strain (Rhizophagus iregularis) has significantly increased root abundance (number of roots) in both sterilized and unsterilized soil and root dry weight in sterilized soil only. However, in unsterilized soil, root dry weight decreased with AMF inoculation. In Walungu acidic soils, P supply could significantly influence the effect of mycorrhizal inoculation on root development and root abundance. AMF inoculation has significantly increased the shoot P concentration when P was supplied. In sterilized soil, mycorrhizal inoculation had a depressant effect on soil phosphorus concentration, especially when P was not supplied.
Conclusion and application of results: Our results suggest that the introduced Rhizophagus iregularis strain increases P uptake in the rhizospheric soil, especially when phosphorus is not applied to the sterilized or unsterilized soil. The use of the Rhizophagus irregularis strain as a biofertilizer could improve phosphorus nutrition and root development in cassava.
Keywords: Arbuscular mycorrhizae, Rhizophagus irregularis, P uptake, Cassava, Ferrallitic soil
Aims: This experiment was done to investigate the effect of adding Rosmarinus officinalis essential oil (REO) in tomato juice and paste during processing in condition of reduced thermal treatment on nutritional qualities and evaluate their postharvest shelf life under Bacillus cereus spore contamination.
Place and Duration of Study: Laboratory of Microbiology, University of Yaoundé I, Cameroon, from January 2017 to June 2018.
Methodology: Total polyphenol content was determined using the Folin Ciocalteu coloric method; the Titatrable acidity and vitamin C content were determined by titration with indicator method. The effect of level of Bacillus cereus contamination, time of thermal treatment and concentration of REO was assessed using a experimental CCD plan. The shelf life was estimated using the storage efficacy of the product on a period of time, and calculated based on the percentage of spoiled products. Data were analysed using XLSLTAT and STATISTICA packages for non-linear regression analyses.
Results: Only 10 min pasteurization at 95°C in the presence of 100ppm of ROE was necessary to totally deactivate 104 Bacillus cereus spores/g in tomato juice while for tomato paste the same concentration of ROE needed 20 min pasteurization at 95°C to totally deactivate up to 108 Bacillus cereus spores/g. Total polyphenols, Titratable acidity and Vitamin C content were affected under this combined processing technique. The storage efficacy of tomato products and hence the extended shelf life was as a result of combined effects between cooking time and microbial load percent reduction that depended on the spore load concentration.
Conclusion: Using Rosmarinus officinalis essential oil can help reduce the thermal impact during tomato juice and paste processing even in condition of high contamination of spores of Bacillus cereus. Moreover in this processing condition, nutritional compounds are not significantly impacted.
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