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Responses to 10 Cycles of Mass Selection in an Inbred Population of Grain Sorghum¹

Retention of genetic variability within highly inbred populations of predominantly self-pollinating plant species suggests that response to directional selection within such populations may be significant. Ten generations of bidirectional mass selection for seed weight, plant height, and days to flower were conducted within a foundation seed lot of ‘Double Dwarf Yellow Milo 38’ (DD38) grain sorghum (Sorghum bicolor (L.) Moench) to evaluate this possibility. Selection gains were evaluated by comparing nonselected and tenth cycle selected populations grown in replicated experiments at three locations in 1978.

Divergence of population means of plus and minus selected strains was significant (p 0.01) for all three traits, while asymmetry of response was significant (p 0.01) for seed weight and days to flower only. Mean per cycle selection response expressed as a percentage of nonselected population mean over 10 generations ranged from 0.25% for the early flowering population to 3.40% for increased seed weight. Realized heritabilities ranged from 0.06 in the early population to 0.17 in the late population. Correlated selection responses were observed for each character selected, but the magnitude and direction of correlated responses were inconsistent.

The results suggest that sorghum populations may respond to directional selection despite apparently restrictive mating systems. Population structure and response to selection in a mixed selling and random mating species like sorghum should be investigated more extensively in relation to the current discussions of population improvement methods.

Key Words: Sorghum bicolor (L.) Moench • Recombination • Outcrossing • Mass selection

² Assistant Geneticist, Dept. of Botany and Plant Sciences, Univ. of California, Riverside, CA 92521; Professor, Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616; and agronomist, The Rockefeller Foundation, New York, NY 10036.

Received for publication June 8, 1979.