Abstract
Mycelia of Penicillium expansum Link and Botrytis cinerea Pers., and also conidia of the former were irradiated with Cobalt-60 gamma radiation. The irradiation took place at Tokaimura Atomic Center (Cobalt source: 1.6×104C), Ibaragi prefecture and Tokyo Metropolitan Isotope Center (Cobalt source: 0.3×104C), Tokyo.
The original cultures of P. expansum and B. cinerea used were isolated from affected apples and strawberries, respectively.
The mycelium samples to be irradiated were prepared by removing the mycelia shake-cultured in potato decoction media (with 2% of saccharose) for 3 days at 25°C, washing them with sterile distilled water, and then suspending them in sterile distilled water in Pyrex tubes. The conidium samples to be irradiated were prepared by obtaining conidia with a sterile needle from a well-sporulating 10-day old culture and putting them in small Pyrex tubes.
After the irradiation, the samples were transferred to potato saccharose agars, being incubated for 7 days at 25°C. The survival of the irradiated samples transferred was confirmed by their resumpted growth on the medium. The temperatures during the irradiation were 19°-24°C.
The results obtained are summarized below:
1. The mycelia of P. expansum and B. cinerea irradiated with the dose of 80×104 rad at a high dose rate (approximately 100×104rad/hr.) were almost completely killed, while the samples irradiated with the same dose at a low dose rate (approximately 2×104rad/hr.) showed resumption of mycelial growth.
2. The minimum doses that lost the conidia of P. expansum the ability to form colony were 40×104 rad at a low dose rate (approximately 1×104rad/hr.), and 20×104rad at a high one (approximatel 40×104rad/hr.), respectively.
3. The irradiation with the doses of 5-40×104rads on the mycelia of P. expansum and B. cinerea delayed their growth and the conidial formation. The sclerotial formation of B. cinerea was also suppressed by the above doses.
4. It should be concluded that the dose rate as well as the dose in the irradiation is one of the factors in determining the sterilizing or fungistatic effect of gamma radiation.
