Genetic variability in quantitative characters induced by thermal neutron treatment of diploid, tetraploid and hexaploid oat seeds

Abstract

Seed lots from 5 oat varieties (Saia, a diploid; P.I. 193958, a tetraploid; and Andrew, Burnett and Pusa, hexaploids) were treated with thermal neutron irradiation, to provide materials for comparing the relative magnitude of variability and the types of mutations induced at different ploidy levels. We grew 40 lines derived from each irradiated population, and a like number from check populations, in a replicated experiment and measured them for heading date, plant height, number of branches per panicle, flag-leaf length, weight per 100 seeds, groat width and groat length. For a few attributes, irradiation treatment caused a significant shift in the population means, and variability was increased for most of the attributes. In general, variability was shifted in both plus and minus directions from the check population means. At the hexaploid level, the mean induced variability from all attributes as measured by genetic coefficients of variation was as great as or greater than that at the tetraploid and diploid levels. Comparisons of the characteristics of the seed-attribute frequency distributions from irradiation derived and check populations tended to show that: (a) mutations occurring in diploid lines produce more discrete expression than those occurring in hexaploids; and (b) a larger portion of hexaploid than diploid lines carry mutations which show some degree of expression. The presence and/or magnitude of genetic variability induced was influenced by the attribute studied, and the genotype treated. No genetic variability was induced for number of branches (except in Pusa variety) and for flag-leaf length; among the hexaploid varieties, Pusa showed nearly twice as much relative variability as the other two varieties. The genetic correlations indicated that the types of mutations induced by irradiation in hexaploids are similar to those induced in diploids; thus, induced genetic variability in hexaploids should be as heritable as that in diploids. Thermal neutron irradiation increased sterility in two of the treated populations. However, there was no evidence that sterility contributed to the apparent induced variability. Intrapopulation correlations, calculated between groat width and sterility, were not significant.