The Relation of Survival to Radiation Dose in Rust Fungi

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Abstract
Radiation dose-survival evaluations were made for urediospores of 4 species of rust fungi[long dash]Melampsora lini, Puccinia graminis f. sp. tritici, P. graminis f. sp. avenae, and P. coro-nata var. avenae. Quantitative inoculation of host plant seedlings and determination of infection counts provided the most useful method of evaluating survival of spores exposed to X-rays, [gamma] -rays, and neutrons; inhibition of spore germination occurred only at dose levels far greater than those required for inhibition of host infection. With UV-light treatments similar survival curves were obtained by either criterion of survival. Sigmoidal survival curves were obtained for all 4 species with each of the radiations used. Deviation of the experimental data from the inactivation model at high LD levels was attributed to a multiprocess system of inactivation. Calculated target numbers for M. lini and P. graminis f. sp. tritici were 4 and 2, respectively. The calculated sensitivity of M. lini spores exposed to X-rays, [gamma]-rays, and neutrons was approximately twice that obtained for spores of the other 3 species; for exposures to UV light the corresponding ratio of sensitivity was 101. Spore sensitivity to UV light, X-rays and [gamma]-rays increased sharply above a spore moisture content of approximately 45%. The X-ray sensitivity of hyphae of M. lini in host infections was approximately 10 times that of spores irradiated at a comparable level of hydration.

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