Abstract
Bacteria and fungi constitute microorganisms which provide essential services to the soil ecosystem, not only for the maintenance of its fertility, but also for the degradation of certain pollutants. The present study was carried out to evaluate the effects of a synthetic fungicide and seed extracts of two fungicidal plants (Anonidium mannii and Ricinus communis) on microorganisms in an agricultural soil sample. With the solvents acetone, water and methanol, seed extracts of A. mannii and R. communis were used for phytochemical screening and for the preparation of solutions with concentrations of 50 µl/ml corresponding to fungistatic doses. For microbial colony enumeration, 10-1 dilutions for fungi and 10-2 dilutions for bacteria were spread on the surface of SCA medium supplemented with recommended doses of the chemical fungicide and 50 µl/ml concentrations of A. mannii and R. communis seed extracts. Petri dishes containing these mixtures are incubated with bacteria at 30°C for 24 hours and with the fungi for 7 days. At the end of each period, the types of microorganisms are differentiated by the colours of the colonies formed. For doses recommended for farmers, the chemical fungicide Monchamp 720WP destroys all bacterial and fungal life on solid SCA agar. In extracts containing abundant alkaloids, bacterial colony counts are low while in extracts containing metabolites, bacterial colonies are high. Different groups of fungi were differentiated by the coloration of the colonies formed. A significant number of fungal colonies of different colours were observed in the presence of extracts containing alkaloids and sterols/triterpenes. Microbial diversity will reduce the bactericidal and fungal activity of the plant extracts used and will favour their multiplication in the media. The inability of these plant extracts to destroy microorganisms continues to provide beneficial ecologically services to the ecosystem which ensures soil fertility and environmental preservation. Thus, the use of these plant extracts ensures good environmentally agriculture
Highlights
Agriculture is an important activity that contributes to the socio-economic development of the population
The study of [72] in vitro, showed that the chemical fungicides Benomyl and Hymexazol inhibited the growth of Fusarium solani and Fusarium oxysporum by more than 80%, but [73] showed that the bacterium Pseudomonas aeruginosa 604 was resistant to the alkaloids contained in extracts of two species of Fumaria genus (F. bastardii and F. capreolata)
At the dose recommended to farmers, Monchamp 720WP destroys pathogenic fungi of crops and microbial life and does not promote bacterial or fungal colony formation in the Starch Casein Agar (SCA) solid agar medium
Summary
Agriculture is an important activity that contributes to the socio-economic development of the population. Agricultural production is highly affected by pests and the plants diseases. To meet the ever-increasing demands of market, yields are improved by the use of chemical pesticides [1], [2]. Domestic sales of synthetic pesticides in Cameroon increased from CFAF 3.6 billion in 1991 to CFAF 12.2 billion in 2000. Due to business agreements with the European Union, the 100% drop in customs duties had led to the intensive importation and use of these chemical. Corresponding author: Manga Anaba Désiré, +237 699938544, 1 Laboratory of Environmental Management and Plant Production, Department of Plant Biology, Faculty of Science, University of Yaounde I, PO Box 812, Yaounde-Cameroon. It should be noted that the continuous use of chemical pesticides impoverishes the soil
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