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Directed Effects of Environment on Populations of Small Grain Varieties¹

Evidence was presented that the effect of environmental stress on a population of oat (Avena sativa L.) and barley (Hordeum vulgate L.) varieties is directed. if random subsets are drawn from a population, then it is expected that the subsets will respond to stress in a similar manner.I t appears, on the basis of limited evidence, that nonrandom subsets will also respond to stress in a similar way, providing the various subsets are not too divergent. Just how great a divergence is permitted before the subsets react differently can probably only be determined by tests. In the case of oats, varieties from Europe, Canada, and northern USA, and from the Corn Belt reacted in a similar manner, indicating a directed effect of environmenot n the subsets.

Subsets drawn from a barley population in a nonrandom manner showed diverse reaction in the case of a split into 6-row and 2-row groups. But when a nonrandom split of the 2-row group into an early and late subset was made, fair agreement between the subsets in their response to environmental change was observed for several traits.

If a directed impact of environment on moderately divergent subsets, such as the change in breeding populations over a period of time, can be demonstrated it will be a means of establishing meaningful genetic correlations. These correlations would be a measure of constancy of a trait at a location over a period of years and would be of use in selection and prediction. It is expected that the hypothesis will apply more to polygenic traits than to traits such as rust resistance.

² Professor, Department of Crop Science, Michigan State University.

Received for publication February 17, 1965.