Evaluation of Ethiopian plant extracts, Acacia seyal and Withania somnifera, to control green mould and ensure quality maintenance of citrus (Citrus sinensis L.)

Abstract

Green mould, Penicillium digitatum (Pers.: Fr.) Sacc., causes economically important postharvest disease in citrus. Materials and methods. Ethiopian plant extracts of Acacia seyal (Del. Var. Seyal) and Withania somnifera (L.) Dual were used to test the control of green mould in wound-inoculated fruit, stored for 21 d at 7 °C and at > 85% RH. The chemical compositions of the two extracts were determined using high-performance chromatography. Thereafter, freshly harvested (naturally infected) fruit were subjected to different postharvest treatments and stored for 50 d to investigate the effects of the two plant extracts on fruit quality parameters. Treatments included (pre-wax + leaf extracts), (wax + leaf extracts incorporated into wax, Citrosol A®), (leaf extract alone), (fruit washed in chlorinated water at 5.25%), (untreated fruit) and (commercially treated fruit). Results. Extracts of A. seyal and W. somnifera reduced the incidence of green mould by 56.1% and 50%, respectively, in wound-inoculated fruit. A. seyal extract contained a high concentration of gallic acid (60.3 mg·mL–1) whilst W. somnifera contained low concentrations of caffeic acid (8.7 mg·mL–1), salicylic acid (6.3 mg·mL–1) and 3,4 dihydroxy benzoic acid (3.8 mg·mL–1). Green mould was absent in naturally infected fruit subjected to (pre-wax + leaf extracts), (wax mixed with leaf extracts) and (leaf extracts) treatments. (Pre-wax + leaf extracts) and (wax mixed with leaf extract) treatments significantly reduced weight loss; retained firmness and colour; and they maintained eating qualities and a maturity index (SSC/TA) similar to commercial treatment. Conclusion. Both extracts of A. seyal and W. somnifera showed potential to be used as an alternative in combined applications with wax application under low temperature storage to replace synthetic fungicides, to ultimately control green mould and retain overall fruit quality.