Radiation-induced polygenic mutation in Arabidopsis thaliana

Abstract

Three experiments were carried out designed to examine further the properties of radiation-induced mutations affecting flowering time in Arabidopsis thaliana and some of the variables which influence these properties, such as the genotype of the variety that was irradiated (first experiment) and the factors which influence the accumulation of mutations within a single inbred line (second and third experiments). The average additive effect of the induced mutations was found to be independent of parental genotype, supporting the view that this property depends on the relation between the particular character studied and fitness rather than the frequency of “plus” and “minus” alleles in the parental genome as suggested by Brock (1965). Considerable response to selection was obtained in families derived by crossing inbred lines which had been previously irradiated and selected, indicating that few of the mutations fixed in these lines were allelic or linked. This result also suggests that each line contained few mutations, each of relatively large effect. Lines which were irradiated and selected every generation showed a linear relationship between response and accumulated dose in both the early and late flowering direction during generations one to five, but a negative response in the early direction and disproportionately large response in the late direction among generations six to nine inclusive. It is suggested that mutations induced in the later generations interact with those fixed in the early generations giving an adverse effect of multiple mutant combinations on fitness. Such interactions may impose limits on the usefulness of induced mutations in plant breeding.