Journal of Biotechnology Research ISSN(e): 2413-3256, ISSN(p): 2413-8878 Vol. 5, Issue. 8, pp: 64-68, 2019 URL: https://arpgweb.com/journal/journal/16 DOI: https://doi.org/10.32861/jbr.58.64.68 Academic Research Publishing Group *Corresponding Author 64 Original Research Open Access Antibacterial Effects of Aqueous Ethanolic Leaf Extracts of Ocimum gratissimum, Cymbopogon citratus, Vernonia amygdalina and Annona muricata on the Isolated Pathogenic Organism of Citrus Canker from Citrus sinensis (Sweet Orange) Eneh Frank Uchenna * Department of Applied Biochemistry, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Okeke Chidi Benjamin Department of Applied Microbiology and Brewing, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Igbokwe Gabriel Ejike Department of Applied Biochemistry, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Okpala Chukwuemeka Obumneme Department of Applied Biochemistry, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Nwachukwu Godslove Pephel Department of Applied Biochemistry, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria Abstract The aqueous ethanolic extracts of Vernonia amygdalina, Ocimum gratissimum, Cymbopogon citrates and Annona muricata were screened for antibacterial activities at 200mg/ml concentration. Antibacterial efficacy of extracts against the bacteria were identified by gram staining techniques, coagulase and catalase tests and the bacterial isolate was indicated by the appearance of clear zones of inhibition around the disks. The extracts of Vernonia amygdalina and Ocimum gratissimum showed inhibitory activities against the bacterial isolate with zones of inhibition of 12mm and 8.5mm respectively while extracts of C.citratus and A.muricata showed no zone of inhibition. Result of the antimicrobial activity of the extracts compared effectively with the activity of standard fumigant with extract of V. amydalina showing the highest potency which was used in preparation of a local fumigant. The minimum inhibitory concentration of V.amygdalina and O.gratissimum were 25mg/ml and 50mg/ml respectively which were not determined in C.citratus and A.muricata. In conclusion, the results of this investigation showed that the aqueous ethanolic leaf extracts of V. amygdalina and O. gratissimum can be used as an effective control measure for the elimination of citrus canker of Citrus sinensis. Keywords: Citrus canker; Gram staining; Biochemical tests; Zone of inhibition; Antibacterial activity. CC BY: Creative Commons Attribution License 4.0 1. Introduction Citrus canker, caused by Xanthomonas axonopodispv. citri (XC) (synonym X. campestrispv. citri ), is a serious disease reducing the external quality of citrus fruits. It affects all types of citrus and severely infects on Citrus sinensis (sweet orange). Canker occurs in all areas where sweet orange grows. Typical symptom on leaves is a raised necrotic lesions surrounding with yellow halo but on fruit and stem halo seldom occurs. Control of the disease requires integrated cultural practices and chemical sprays. Copper compound products are recommended for canker control. One major limitation of using chemical control agents is that phytopathogenic bacteria frequently develop a resistance to these compounds [1]. In recent years, much interest has been developed in the antimicrobial effects of medicinal plants for plant disease control. Some plant extracts were reported as effective inhibitors of phytopathogenic bacterial growth and X. axonopodis was also suppressed by plant extracts [2]. There is growing interest in exploiting plants for medicinal purposes especially in Africa, as microorganisms are developing resistance to many drugs thereby creating situations where some of the common and less expensive antimicrobial agents are loosing effectiveness [3]. Herbal medicine which uses medicinal plants primarily presents as an alternative to such situation [4]. These medicinal plants have immensely contributed to the development of human health and welfare. Concomitantly, there is an increase in data and huge patronage to herbal products round the world [5]. Medicinal plants such as Ocimum gratissimum, Cymbopogon citratus, Vernonia amygladina and Annona muricata have been asserted to provide various culinary and medicinal properties. These medicinal properties exert bacteriostatic and bacteriocidal effects on some bacteria. These effects have been attributed to the peptides, alkaloids, essential oils, phenols and flavonols which are major components in those plants mentioned above [6].