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Changes in Alfalfa Cultivars Grown in a Semiarid Environment¹

Eight alfalfa (Medicago falcata L. and M. sativa L.) cultivars were seeded on a semiarid dryland site in 1954. In 1979 open-pollination seeds were harvested, plants were excavated to produce synthetics, and seeds of old stocks were obtained for use as check populations to determine if significant changes in adaptive traits had occurred over the 25 years since establishment. Flower color, emergence of seedlings with limited water and from excessively deep plantings, seedling root length, and the recovery and survival of seedlings following a laboratory drought exposure test were evaluated. No significant changes in flower color were found between the checks and the open-pollination or synthetic populations although a slight tendency for a higher frequency of blue to purple flowers occurred. Seedling emergence with limited water, seedling emergence from excessively deep plantings, and seedling root length were all greater for open-pollination and synthetic populations than for the check populations. Surprisingly, however, recovery and survival of seedlings following laboratory drought tests were lower for the open pollination and synthetic populations. Thus, although genetic changes have definitely occurred over the 25-year life of this stand, it is not certain whether these changes were due to natural selection pressures or to the relative reproductive capacities of M. falcata and M. sativa.

Key Words: Medicago sativa L. • M. falcata L. • Drought resistance • Natural selection • Root depth • Adaptation • Seedling emergence

² Authors are research geneticist and plant physiologist, USDA-ARS, Crops Res. Lab., Utah State Univ., UMC 63, Logan, UT 84322.

Received for publication July 29, 1982.