IMPACT OF SEASONAL CHANGES ON THE DISTRIBUTION AND PATHOGENICITY OF Aspergillus flavus ON DRIED FERMENTED COCOA BEANS IN SOUTHWESTERN NIGERIA

Abstract

This study aimed to determine the distribution and pathogenicity of fungi populations associated with stored cocoa beans in dry and wet environmental conditions within southwestern Nigeria. Dried fermented cocoa beans were collected from randomly selected cocoa stores in Ibadan, Ijebu Igbo, Ile Ife, Akure and Ado Ekiti in Oyo, Ogun, Osun, Ondo and Ekiti States, respectively during dry and wet seasons. Fungi associated with the beans samples were isolated, identified and pathogenicity of the most occurring species was determined. Aspergillus flavus (4.76-88.24%), A. niger (7.69- 100.00%) and Rhizopus spp. (7.14-81.81%) were mostly isolated from the cocoa beans samples stored under the two storage conditions. Six out of the thirteen moulds isolated from the collected beans samples from across the states, were Aspergillus species. Other isolated moulds include Fusarium spp. (7.69 – 100.00%), Rhizopus spp. (8.33 – 81.81%), Neurospora spp. (6.25 - 22.22%), Pythium spp. (18.18 – 58.33%) and Trichoderma spp. (50.00%), Penicillium sp. (8.33 – 15.38%) and Lasiodiplodia theobromae (9.09 – 81.81%). Also, only two out of the 46 A. flavus dry-season isolates showed high pathogenicity, while one isolate did not show visible symptom of seed infection. Similar trend was observed on the remaining fifty-four (54) wet season Aspergillus isolates. Aspergillus spp. and Rhizopus spp. were mostly associated with dried fermented cocoa beans at storage in Southwest Nigeria. Most strains of A. flavus were however able to cause varying degrees of infections on stored cocoa beans both during dry and wet seasons of the year. Further work however need to be done, to find lasting solutions to the problem of fungal and mycotoxin contamination of dried fermented cocoa beans at storage.