Spontaneous and induced mutation rates in di-, tetra-, and hexaploid oats (Avena spp.)

Strains of di-, tetra-, and hexaploid oats derived from untreated and EMS-treated seeds were used to estimate mutation rates for spontaneous and induced mutations at loci that affect quantitatively inherited traits. The oat strains were produced by using a dichotomous progeny scheme.

The study was initiated with one plant from each of two cultivars for each ploidy level. From a first-generation plant, four seeds were chosen to produce second-generation plants. Two were sown without treatment, and the other two were treated with 0·04 M solution of ethyl methanesulfonate (EMS) for four hours. For the third and subsequent generations, two progenies were grown from each plant in the previous generation. Seeds in the treated line of descent were given EMS through generation 5. Both lines of descent were carried through six generations. The 125 strains (62 in the untreated line of descent, 62 in the treated line of descent, and one from the original plant) from one cultivar were sown in a field experiment and traits measured were grain yield, heading date, plant height, flag leaf length, number of spikelets per panicle, 100-seed weight, seed width, seed length, and protein percentage.

A mutation was judged to have occurred when two criteria were met: (a) the observed value for a trait of a parent strain differed from comparable values in one or both of its progeny by an LSD unit and (b) the deviant value was inherited into later generations. Mutation rates were expressed as mutations per trait per 100 gametes.

Genotypes differed with respect to the rates of occurrence of spontaneous and induced mutations. There was no obvious relationship between spontaneous and induced mutation rates that genotypes showed, but mutability was trait related. Traits most susceptible to mutation induction were grain yield, heading date, plant height, number of spikelets per panicle, and seed length.

Spontaneous mutation rates for di-, tetra-, and hexaploid oats were 1·2, 0·5, and 0·3 mutations per trait per 100 gametes, respectively, whereas induced mutation rates were 1·2, 1·3, and 2·0 mutations per trait per 100 gemetes, respectively.