In vitro Antifungal Potential of Aqueous Seeds Extracts of Azadirachta indica and Thevetia peruviana against Phytophthora megakarya in Cameroon

This study aims to evaluate the antifungal effects of aqueous extracts of Azadirachta indica (AEAI) and Thevetia peruviana (AETP) seeds taking it from a biological perspective under laboratory conditions. A randomized sample block design containing four treatments (T-: absolute control, AEAI, EATP and Ridomil Gold Plus at the dose of 3.33 mg/ml) in three repetitions was used. Plant extracts were used in three concentrations: C1: 12.5 μl/ml; C2: 25 μl/ml and C3: 50 μl/ml. The study took place in University of Yaounde 1, Faculty of Sciences, Department of Plant Biology, laboratory of Phytopathology and Microbiology in Cameroon, during the years 2013-2014. The chemical screening and the chromatographic profiles of the extracts, the aggressiveness of the P. megakarya strains, the inhibition of the strains by the extracts, the minimum inhibiting concentration (MIC50 and MIC90) and the extract characteristic were determined by the usual phytochemical and phytopathological methods. Obtained results show that seed extracts of both plants contain many chemical compounds such as sterols, sugars, alkaloids, anthraquinons, saponins, coumarins, and fatty acids. The two extracts in high concentrations (50 μl/ml) induced an inhibition rate of 100% on the mycelium growth of all the strains tested. Using the extract in concentration C2, the inhibition rate varies from 42.5 to 100% and from 27.0 to 88.0% respectively for AETP and AEAI. The values of MIC50 and MIC90 registered were 0.48, 2.63 μl/ml for AETP, 4.76 and 19.11 μl/ml for AEAI, indicating that AETP is more efficient when compare with AEAI. At concentrations C3 and C2, these two extracts indicated a fungicide effect, while at a weaker concentration the effect was fongistatic. This study shows that at high concentrations, the efficiency of AETP and AEAI seems to be the same with the one of Ridomil Gold Plus in the repression of P. megakarya growth in vitro. These natural substances can be integrated in control program of this P. megakarya strains in Cameroon.