Samples of soil were exposed to gamma radiation from a Co60source. By a modified soil-plate technique fungi were isolated from the radiation-treated soils and compared to those isolated from untreated soils. At intensities of 250, 500, 750, and 1000ensp;kr, 2.53, 0.67, 0.10, and 0.04, respectively, of the viable propagules of fungi survived. Twenty-eight species of fungi survived soil irradiation of 250ensp;kr or more, many of which were not isolated from untreated soil. Prior gamma irradiation of soil samples enabled isolation of certain fungi that occur in soils in low numbers and that are not ordinarily found on conventional dilution or soil plates. Most of the members of the Moniliaceae, comprising a large portion of the soil fungal population, were killed by radiation, but the Dematiaceae generally were more resistant. It was found that resistance of certain fungal spores in soil to high intensity radiation is related to growth rates of mycelium in pure culture under sublethal levels of continuous radiation. The mycelium of three resistant fungi, which originally survived high doses of radiation, grew better under chronic irradiation than did two susceptible fungi, which were killed by high doses of soil irradiation.
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