Effects of Gamma Irradiation on Post-Harvest Deterioration of Cassava (Manihot esculenta Crantz) Tuber by Fungi

摘要

Three varieties of cassava (Manihot esculenta Crantz) (SMS 909-25, COL 2215 and COL 1734) that were gamma (y) irradiated and non-y irradiated were investigated for susceptibility to post-harvest fungal rot by five species of moulds (Botryodiplodia theobromae, Penicillium oxalicum, Aspergillus niger, Fusarium solani and Macrophomina phaseolina). These moulds were inoculated into tuber samples at wound depths of 10 mm with either single or paired cultures. The inoculated samples were stored in two environments (ambient temperature (26 ± 2°C) and polyethylene bags of 18 um thickness). The most extensive rot development at ambient temperature was 13.50 ± 0.10 mm by M. phaseolina for single cultures while pair-cultures of P. oxalicum and M. phaseolinaproduced 19.50 ± 0.05 mm in irradiated cassava COL 2215 but 15.50 ± 0.71 mm by M. phaseolina for a single culture and 21.50 ± 0.71 mm for pair-culture of P. oxalicum and M. phaseolina in non-irradiated cassava. The minimum rot of 6.50 ± 0.05 mm by P. oxalicum and 13.00 ± 0.00 mm by B. theobromae and A. niger occurred in irradiated cassava COL 1734 but P. oxalicum produced 8.50 ± 0.71 mm while P. oxalicum and F. solani produced 13.75 ± 0.72 mm in non-irradiated cassava. Generally, significant (P>0.05) rot was recorded for non-irradiated than irradiated cassava varieties analyzed. In polyethylene bags storage, generally the highest zone of rot of 16.50 ± 0.05 mm by M. phaseolina and 21.63 ± 0.03 mm by P. oxalicum and M. phaseolina were observedin COL 2215. M. phaseolina showed the highest zone of rot development in y and non-y irradiated cassava varieties irrespective of the storage condition.