Chromosome aberrations, changes in DNA content and frequency and spectrum of mutations induced by X-rays and neutrons in polyploids

Abstract

A study of the relationship between polyploidy and radiation sensitivity was carried out in diploid, tetraploid and hexaploid species of wheat and in diploid and auto-tetraploid barley using X-rays and fast and thermal neutrons as radiation sources. Survival, frequency of chromosome aberrations, DNA content of nuclei, seed fertility and frequency of mutations in the second and third generations were used as indices of radiosensitivity. Survival was better in 4x barley in comparison with the diploid in X-ray treatments, while an increase in radiation resistance with an increase in chromosome number was evident in the wheat series with fast neutrons. Data on the frequency of chromosome aberrations and reduction in DNA content observed in root-tip nuclei indicated a possible interaction between polyploidy and the LET of the radiation employed. Seed fertility was less affected in polyploids than in diploids. The frequency of chlorophyll mutations decreased with increasing ploidy in both wheat and barley while the frequency of viable mutations registered the opposite trend in wheat. Recessive mutations could be detected in 4x barley only in the M₃ generation. The relative proportion of chlorophyll and morphological mutations observed in 4x barley during the M₃ generation was similar to that found in 6x wheat in M₂ and M₃ generations. Though a high frequency of viable mutations was observed in 6x wheat, the spectrum of the induced variation was very narrow thereby indicating that this species is a functional diploid only for a few loci.