RELATION OF POLYPLOIDY TO HEAT AND X-RAY EFFECTS IN THE CEREALS*

Abstract

The expts. were chiefly concerned with emphasizing differences between the effects of heat and X-rays. It was confirmed that X-ray tolerance of dormant seeds increases with chromosome number and demonstrated that tolerance for heat is independent of chromosome number. In tests combining heat and X-rays in successive treatments, heat treatment of dormant seeds preceding irradiation decreased the injury, while heat treatment following irradiation increased the injury resulting from irradiation. In another comparison with diploid wheat it was found that heat treatments had little, if any, effect on mutation frequency, which was in contrast with the results from trials with X-rays. In another comparison heat had little effect on the production of chromatic bridges in root tips. X-rays had a marked effect in producing bridges and the frequency increased with chromosome number. Similar results were obtained in a comparison of the effects of heat and X-rays on the production of translocations. In an expt. to determine the relation between number of chromosomes in mature pollen of wheat and frequency of X-ray effects, it was found that the frequency of recovered translocations, complex rearrangements, and deficiencies increased markedly with polyploidy.