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Loss of Half-Sib Families in Mass Selection¹

To study the loss of half-sib families in mass selection, progenies of seven populations of Pensacola bahiagrass (Paspalum notatum var. saure Parodi) being improved by recurrent restricted phenotypic selection (RRPS) were studied in detail. Accession numbers assigned to progenies of selected plants recorded in spaced-plant field plans of randomized populations of 990 to 1200 plants per cycle permitted a determination of half-sib families lost with each cycle of grid selection. Loss of half-sib families averaged 31.2% per cycle for five populations when the top yielding five plants in 25-plant blocks were selected in a planting with six randomly placed plants of each family in a population. With only five randomly placed plants of each family, the loss of half-sib families increased to 38%. Loss of these low yielding half-sib families permitted more rapid progress than a plant-to-row breeding system that would have retained them. In 35 computer-generated populations with six randomly placed offspring from each of 42 selections, reducing the percent of plants selected from 25.0 to 8.3, increased the percent of half-sib families lost from 20.3 to 61.2. In four populations that lost 31% of their half-sib families, 51% of the remaining families were recovered only once whereas 3.3 and 0.8% were recovered four and five times, respectively. Because half-sib families recovered most frequently were the most productive, mass selection as practiced here permitted more rapid advance than a breeding system requiring equal representation from each family in the polycross for the next cycle.

Key Words: Pensacola bahiagrass • Paspalum notatum var. saure • Recurrent-restricted-phenotypic-selection (RRPS) • Spaced-plant-population-progress (SPPP)

² Research geneticist, USDA-ARS, and the Univ. of Georgia, College of Agric. Exp. Stns., Coastal Plain Exp. Stn., Agronomy Dep., Tifton, GA 31793.

Received for publication May 29, 1984.