Embree, Robert W. (U. California, Berkeley.) Radiomyces, a new genus in the Mucorales. Amer. Jour. Bot. 46(1): 25‐30. Illus. 1959.—Radiomyces spectabilis is described as a new genus and species in the order Mucorales of the Phycomycetes. This fungus readily grows in pure culture, and developmental stages of the asexual and sexual reproductive structures are described. The genus is referred to the family Thamnidiaceae, and in doing so, the family concept is necessarily broadened to include almost colorless, smooth‐walled zygospores with appendiculate suspensors.

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The comparative virulence of thermotolerant Mucorales was determined for cortisone-treated and untreated Swiss mice by intravenous administration of spores. The measure of virulence was based on an LD50 value, calculated after the 30-day observation period. Of the known etiological agents of mucormycosis, Mucor meihei, M. pusillus, Rhizopus arrhizus, R. chinensis, R. cohnii, R. microsporus, R. oryzae, R. rhizopodiformis and Cunninghamella elegans were able to produce fatal infections in mice; whereas, Mucor alternans, M. ramosissimus and Syncephalastrum racemosum were avirulent at dosages of up to 10(5) spores. Of those thermotolerant species which have not been reported to cause mucormycosis in human beings, Radiomyces embreei, R. spectabilis, Rhizopus oligosporus and Thermomucor indicae-seudaticae were found to produce fatal infections in mice; whereas, an isolate of Mycotypha africana was avirulent. Cortisone treatment of mice was found to lower their resistance to infection at a given spore dosage as measured by ET50 values.

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