Antifungal Potential of Aqueous Extracts of Neem Seeds (Azadirachta indica) on the vitro Development of Six Strains of Phakopsora pachyrhizi, Causal Agent of Asian Soybean Rust

A study carried out in the University of Yaoundé I (Cameroon) aimed to evaluate the effect of aqueous extracts of neem seeds (Azadirachta indica) on the in vitro development of Phakopsora pachyrhizi. The experimental set-up was a completely randomized blocks design containing six treatments: T0 (control), T1, T2, T3 and T4 (consisting of 12.5, 25, 50 and 100 µg/ml of extract respectively) and T5 (5.33 µg/ml of Plantineb 80 WP). Six strains of P. pachyrhizi were used. The phytochemical screening of the aqueous extract of neem seeds (AENS), the effect of the extract on the fungi growth, the minimum inhibitory concentrations (CMI50 and CMI90) and the characteristics of the extracts were determined by phytochemical and phytopathological methods. The results show that the AENS contains a varied range of chemical compounds such as sterols, sugars, alkaloids, saponins and terpenoids. The highest concentration of the tested extract (100 μg/ml) induced a total inhibition (100%) of the fungi growth. For all strains, the concentration of the extract was fungicidal. The inhibition percentage was proportional to the different doses of the tested extract and varies between 31.2 to 71.4% depending on the strains. MIC 90 was 81.8, 82.8, 83.7, 82.9, 84.4 and 84.8% for the F.Mi, F.Nko, G.Mi, G.Nko, Gr.Mi and Gr.Nko strains respectively. Thus from this study, the efficacy of high doses of AENS is similar to that of Plantineb 80 WP in the in vitro control against P. pachyrhizi. This substance could thus be included in the control program for the pathogen.