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Influence of Drought Stress on Genetic Variances of Alfalfa and Wheatgrass Seedlings¹

Sprinkler irrigation gradient systems may be useful for screening plant populations for drought resistance. To be effective, traits chosen as measures of drought resistance must be heritable throughout the range of stress environments represented by the moisture gradient. Line source gradient techniques were used to evaluate the potential of these techniques in screening two forage crops for seedling drought resistance and to examine the effect of irrigation gradients on important genetic parameters. Stand densities and/or shoot dry weights were measured on populations and progenies of alfalfa (Medicago sativa L.) and a wheatgrass hybrid [Elytrigia repens (L.) Nevski x E.spicata (Pursh) D.R. Dewey] grown in five experiments under greenhouse and field irrigation gradient systems. The means, genetic variances, broad sense heritabilities, and predicted genetic gains due to selection declined as the amount of supplemental water was reduced. Most of the phenotypic variance observed in the drier sections of the plots was environmental in origin. When water application gradient systems are used in breeding for drought resistance, the target environments must be carefully delimited. Gains due to selection may be more rapid if selection is made at intermediate rather than at extreme levels of drought stress.

Key Words: Elytrigia repens • Elytrigia spicata • Agropyron repens • Agropyron spicatum • Interspecific hybrid • RS hybrid • Heritability • Medicago sativa • Line-source sprinkler

² Research geneticists and plant physiologist, USDA-ARS, Crops Res. Lab., Utah State Univ., UMC 63, Logan UT 84322.

Received for publication June 27, 1983.

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