Genetic Effects of Ultra-Violet Radiation in Maize

Abstract

A high voltage mercury discharge tube of fused quartz emits radiation consisting chiefly of X 2537. A commercial tube of this sort (Hanovia (Sc-2537), operated at 5000 volts and 100 m. a., was used as a source of radiation in comparison with filtered radiations of the types described in the preceding paper. The discharge tube treatments were applied under conditions similar to those used with the mercury arc. Exposures were made at the same distance and with the same filter cell, with 1 cm. of distilled water in place of the filters used with the mercury arc. Under these conditions about 83% of the total intensity is X 2537. Other wave-lengths included are chiefly in the near ultra-violet and visible. Of the wave-lengths shorter than X 3130, more than 97% of the total intensity is X 2537. For the purposes of genetic experiments, therefore, this radiation is almost monochromatic X 2537. The ratio of intensity of the radiation from the discharge tube and the arc (the water filter being used in both cases) was for X 2537 approximately 1: 1, for total radiation shorter than X 3130 approximately 1:8. In experiments with the discharge tube, the multiple recessive seed parent used was A a C c wx wx su su pr pr y y. The pollen stock carried the dominant alleles of all of these genes. It was therefore possible to detect one-half of the losses of A and C (as indistinguishable color losses) and all of the losses of Wx, Su, Pr and Y. The maximum dose tolerated is considerably lower than the maximum tolerated dose of the filtered radiations reported above. Only the most approximate comparisons may be made in tolerance because of the variation with environmental conditions which has been mentioned. In treatments with the discharge tube, under favorable weather conditions and with excess pollen, well-filled ears are produced by the use of pollen irradiated for 30 seconds or less, but only partial seed setting occurs with pollen irradiated 60 seconds or more. A few seeds are produced by the use of pollen treated as long as 120 seconds. Under similar conditions, with filtered radiation A of the mercury arc (described in the preceding paper), well-filled ears are produced by the use of pollen irradiated 2 minutes and sometimes 4 minutes, and a few seeds are produced by pollen treated as