Antifungal Potential of Acetone and Ethyl Acetate Extracts of Thevetia peruviana on Development of Phytophthora colocasiae, Causal Agent of Late Blight of Taro (Colocasia esculenta (L.) Schott) from Three Agro-Ecological Zones of Cameroon

Aims: This study was aimed to evaluate the antifungal activities of acetone and ethyl acetate extracts of Thevetia peruviana seeds on the in vitro growth of the fungus.

Study Design: A randomized sample block design containing four treatments (T- = Negative control; T2= Ethyl acetate extract; T3= Acetone extract; T+=Callomil Plus) with three repetitions was used. Plant extracts were used at three concentrations: C1: 12.5 µl/ml; C2: 25 µl/ml and C3: 50 µl/ml; the chemical fungicide at the dose of 12.5 μL/ml.

Place and Duration of Study: The study was conducted in the University of Yaoundé 1, Faculty of Sciences, Department of Plant Biology, Laboratory of Phytopathology and Crop Protection, and in the Institute of Agricultural Research for Development (IARD) of Yaoundé, Laboratory of Phytopathology, during the year 2019-2020.

Methodology: acetone and ethyl acetate extracts of T. peruviana were prepared and used at concentrations of 12.5, 25 and 50 µl/ml. P. colocasiae was isolated from infected taro leaf cultivars "Macumba or Ibo coco" located in three different regions: west, Littoral and Centre. The various explants were were put in V8 agar medium and maintained in pure culture. Mycelial fragments of P. colocasiae of about 0.8 cm in diameter were cut and placed in sterile Petri dishes containing Potato Dextrose Agar (PDA) medium supplemented with different concentrations of plant extracts and incubated at 23±1°C for seven days for the evaluation of the radial growth.

Results: The results obtained showed that the acetone and ethyl acetate extracts have completely inhibited the growth of the strain of West at 25 μ/ml while total inhibition of the pathogen was not obtained with strain of Centre region. The lowest inhibition was obtained with the strain of Littoral region: 93.88 % for acetone extract and 90.78 % for ethyl acetate extract compare to 100 % for west and Centre region at highest concentration.

Conclusion: The acetone and ethyl acetate extracts at the concentration of 25 μ/ml totally inhibited the in vitro radial growth of some strains of P. colocasiae. These extracts, which are effective against P. colocasiae, may substitute fungicides in the fight against taro leaf blight.