Characterization of Botryodiplodia Theobromae Isolates Affecting Cocoa, Mango, Banana and Yam in Ghana

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Botryodiplodia theobromae is a very important pathogenic species on many food and tree crops causing significant yield losses. The fungus has been reported to have a wide host range. This study was conducted primarily to establish some of the host range characteristics of the species in Ghana. Twenty-five isolates of B. theobromae obtained from cocoa, mango, banana and yam from some agro-ecologies in Ghana were maintained on potato dextrose agar (PDA) and used to - 5 - inoculate healthy matured cocoa pods and mango fruits. Symptoms of rot characteristics of the species resulted from inoculation with mycelia of the isolates. B. theobromae isolates from cocoa, mango, banana and yam used in the inoculation experiments were not different in their infections on the two crops inoculated. Morphological characteristics of single-spore cultures of the 25 isolates were compared on PDA at 28C. All the isolates produced black pigments in culture 48 hrs after inoculation. Based on growth rates on PDA, the isolates were separated into four groups. The growth rate ranges were 0.93 to 0.94 mm/hr, 0.91 to 0.92 mm/hr, 0.82 to 0.90 mm/hr, and 0.72 to 0.76 mm/hr. The relatedness of the 25 isolates was investigated at the molecular level using SSR and RAPD primers. Two isolates, B(Kt) and B(Ef), both from banana fruits shared the highest genetic similarity of 83% with all others measured below 75%. The isolates studied were not host specific and ecologically non-specific. Molecular analysis of the isolates indicates that several strains of B. theobromae exist in Ghana.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of Master of Science Degree in Biotechnology