| Popis: |
A second cycle of thermal neutron irradiation for expanding the genetic variability for 3 polygenic attributes, relative to the pedigreed procedure and relative to the first cycle of irradiation, was evaluated in 4 oat populations: irradiated Clintland; irradiated Beedee; the hybrid of Clintland x Beedee; and the irradiated hybrid. The 5 lines with the highest 100 seed weight from each population were re-irradiated and also pedigreed. The sampling procedure involved populations; parents within populations; families within parents; and lines within families. Lines derived from populations by these 2 methods and lines from the original populations were grown in a replicated experiment, and were measured for 100-seed weight, heading date and plant height. The progress from selecting the parent strains for 100-seed weight was as great as or greater than that predicted in both the irradiation-derived and the hybrid-derived material. For both the selected (seed weight) and unselected (plant height and heading date) attributes, the new populations developed via recurrent irradiation showed expanded variability over either the original or the pedigreed populations. However, the second irradiation treatment did not generate as much variability as the first. There were no significant shifts in the population means as a result of the re-irradiation treatment. For all attributes, the variances, generated from treating hybrid-derived materials with either one or two doses of irradiation, were somewhat smaller than the sum of hybridization- and irradiation-derived variances which had been estimated independently. The degree of conformity between the actual and predicted variance was attribute-oriented. |
