Monascus pigments (MPs) possess a range of biological activities, such as antimicrobial and potential anti‐obesity activities. A lot of Monascus strains are used to produce MPs. In this study, the effect of radiation on pigment production and morphological changes of the fungus was investigated. The spore suspensions were exposed to different doses of Gamma by a Co‐60 –irradiator and then cultured on potato dextrose agar. Some changes including widening, thickening, intertwining, swelling, and chlamydoconidia production were investigated. The amounts of pigments production were separately determined by measuring the absorbance in three different wavelengths. The highest changes and pigment production was obtained for spore suspension treated at a dose of 1 kGy. The results showed that Gamma irradiation had significant effects on mycelial morphology and subsequently pigment biosynthesis. The morphological changes in terms of hyphal diameters exhibited a correlation with pigment production.

Very few studies are available on the effect of gamma irradiation on the fungus Monascus purpureus. In this study, the effect of gamma irradiation on morphological, physiological and pigment production changes and the interaction of these factors with each other was studied and this is one of the novelties of this study. The results of this study showed that:

• Gamma irradiation causes morphological and physiological changes in Monascus purpureus.
• Changes in the structure and diameter of the hyphae of Monascus purpureus cause a change in the amount of pigment production.
• Monascus pigments can be used as a substitute alternative for synthetic pigments in the food industry.