The Relationship of the Efficiency of Energy Conversion Into Growth as an Indicator for the Determination of the Optimal Dosage for Mutation Breeding With the Appearance of Chromosomal Bridges, Ring Chromosomes, Micronuclei and Incomplete Mitosis After Gamma Irradiation of Kernels of Triticum Turgidum Ssp. Durum L. Cultivar Orania
Abstract BackgroundA 50% growth reduction of seedling height (GR50) after acute gamma irradiation of dormant kernels is widely used as a measure of irradiation damage to obtain the ideal irradiation dosage for mutation breeding. It became clear in recent years that the GR50 is not sensitive enough to predict the ideal gamma irradiation dosage for mutation breeding and it predicts a value that is higher than ideal. The study aim was to determine whether root, shoot and seedling growth on the one side and the efficiency of energy conversion into growth on the other are measuring different growth retardation effects of gamma irradiation that are the result of DNA damage (bridges, ring chromosomes, micronuclei, incomplete mitosis) in Triticum turgidum ssp. durum. If the efficiency of energy conversion into growth is measuring different effects, the usefulness of efficiency of energy conversion into growth to predict the optimal dosage for mutation breeding will be investigated. ResultsThe kernels were gamma irradiated from 50 - 350 Gy using a 60Cobalt source. The kernels were left to germinate and grow for a period of 132 hours for the shoot and root growth and the efficiency of energy conversion into growth determination and for a period of 47.5 hours for the determination of the number of bridges, ring chromosomes, micronuclei and incomplete mitosis. The control differed highly significantly from 50 Gy and higher dosages and from 250 Gy and higher dosages for root and shoot growth respectively and from 250 Gy for the efficiency of energy conversion into growth. There was a highly significant increase in the number of bridges and micronuclei between 50 Gy and 150 Gy together with the higher irradiation dosages and only from 250 Gy for the ring chromosomes and interphase cells with incomplete mitosis. Root and seedling growth on the one hand and the efficiency of energy conversion into growth on the other were found to be measuring different effects of gamma irradiation on plant growth. ConclusionThe optimal dosage for mutation breeding was determined by making use of the efficiency of energy conversion into growth.