Twenty Years of Reciprocal Recurrent Selection with Two Synthetic Varieties of Maize (<i>Zea mays</i> L.)¹

Abstract

Five cycles of reciprocal recurrent selection in two synthetic varieties of maize ( Zea mays L .) were summarized. Yields of the varietal cross and one parental variety were increased significantly, but the yield of the other variety de, creased slightly. Expected gain in the varietal cross yield, calculated from pooled heritabilities and selection differential, was 7.2% per cycle, but observed gain was only 1.7% per cycle. In the sixth cycle, selection among S 1 plants was substituted for selection among S 0 plants. Selection within the randomly mated varietal cross was initiated for comparison with selection within the two parental varieties individually. Estimates of genetic variance within the parental populations in the sixth cycle were higher than for the three previous cycles, and genetic variance was higher within the randomly mated varietal cross than within the parental varieties.