Antifungal Activity of Annona muricata Seed Extracts Against Cercospora malayensis, Causal Agent of Cercospora Leaf Spot Disease of Okra (Abelmoschus esculentus L.)

Background: Cercospora leaf spot disease of okra whose pathogen is Cercospora malayensis causes yield losses of up to 60% in plantations. To limit productivity losses, fungicides are commonly used, but are expensive and degrade the environment.

Aims: This study aims to test in vitro efficacy of Annona muricata seed extracts against Cercospora malayensis.

Study Design: Four extracts were used in this study (the ethyl acetate, acetone, methanol and aqueous extract of A. muricata seeds at the concentrations C1 = 7.5 μl/ml, C2 = 15 μl/ml, C3 = 30 μl/ml and C4 = 60 μl/ml as well as the synthetic fungicide at the concentration of 3.33 g/l) in triplicate. The phytochemical screening of the extracts was performed, the radial growth of pure explants (7 mm diameter) of C. malayensis deposited in sterile Petri dishes containing the PDA medium supplemented with the different concentrations of extracts and incubated at 23 ± 1°C for 6 days were evaluated. Minimum inhibitory concentrations (MIC50, MIC90) were calculated.

Results: The extracts of A. muricata seeds are rich in tannins, flavonoids, terpenoids and phenols. The ethyl acetate extract at the concentration C3 resulted in 100% total inhibition of growth of C. malayensis in the Petri dishes. The other extracts resulted in total inhibition of the growth of C. malayensis at C4. The low MIC50 values (12.9 and 21 μl/ml) were obtained with the ethyl acetate and acetone extract, respectively. The ethyl acetate and aqueous extract at the C4 concentration were found to be fungicidal.

Conclusion: The extracts were found to be potential fungicide against the C. malayensis strain and might be an alternative in the fight against fungal diseases of okra as their activity was comparable to that of the synthetic fungicide Monchamp 72 WP.