Incidence of Lasiodiplodia theobromae and other Fungi in Kolanuts (Cola nitida and Cola acuminata) in Nigeria

Abstract

Aim: A study was conducted to determine the frequency of occurrence of fungi associated with kolanuts (Cola nitida and Cola acuminata) at processing and storage. Methodology: Healthy and infected kolanuts (Cola nitida and Cola. acuminata) collected randomly during processing and storage from various locations in Nigeria were used in this study. Infected kolanut samples were plated on potato dextrose agar (PDA). The plates were incubated at 250C and the incidence of associated fungi was recorded after 5-10 days depending on when growth could be observed. The fungal colonies emerging from the tissue piece were hyphal-tip-transferred onto new PDA plates to obtain pure cultures. Results: Lasiodiplodia theobromae, Fusarium pallidoroseum, Fusarium moniliforme, Fusarium cacispermum. Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus and Paecilomyces variotii were obtained from the infected kolanuts. The means frequency of occurrence of Lasiodiplodia theobromae on Cola nitida and Cola acuminata ranged between 40-47% and 33.5-40% respectively. The mean frequency of occurrence of other isolated fungi ranged between 3-14% on both species of Cola. The pathogenesis tests established Lasiodiplodia theobromae as the causal pathogen of black rot disease of kolanuts. When kolanuts were artificially wounded before inoculation with Lasiodiplodia theobromae, 79.2% infection was recorded compared to 33.3% infection recorded in unwounded nuts. A highly significant positive correlation (r2 = 0.8844) existed between wounding of nuts and incidence of black rot diseases. Conclusion: The present study established that kolanuts were susceptible to fungal infections. This study confirmed the occurrence of storage rot fungi on kolanuts in all the locations of sampling, which represent the rain forest and guinea savanna zones of Nigeria.