Successive growth of gamma irradiated Aspergillus flavus strains isolated from nutmeg kernels (Myristica fragrans)

Abstract

Aspergillus flavus is one of the important fungus which can cause nutmeg deterioration during storage. The study aimed to investigate the effect of gamma irradiation 5 and 10 kGy on conidial germination and successive growth Aspergillus flavus strains isolated from nutmeg kernels up to 20 generations. Thirteen strains of the A. flavus were sub-cultured in potato dextrose agar (6 days, 28 °C). Conidia of each strain were harvested and one mL (10 7 conidia per mL) in 1.5 mL eppendorf tube were centrifuged 6000 ×g, air-dried (24 h, 28 °C) and irradiated at 5 and 10 kGy. Experiments were done in triplicate for each irradiation dose. Conidia with no irradiation used as control. After irradiation, conidia were re-suspended in 1 mL sterile distilled water. Serial dilutions were made and plated onto Aspergillus flavus and Parasiticus agar. Morphological characteristics such as colony diameter, mycelial branches, conidiophore and mycelial growth up to 20 generations were compared between irradiated and non-irradiated strains. Results showed that gamma irradiation up to 10 kGy inhibit conidial germination and mycelial growth of surviving strains. Successive growth of irradiated A. flavus up to 20 generations showed that their colony tend to grow and recover to their normal growth.