Mass selection for improvement of grain yield and protein in a maize population

Increasing grain protein concentration in maize (Zea mays L.) has not been a major focus of most breeding programs, which mainly focus on yield, maturity, and resistance to stress. The objective of this study was to evaluate the effectiveness of three cycles of mass selection to improve simultaneously yield and grain protein in the maize population GR-OP-319, derived from the F-2 generation of the single-cross hybrid PX-95. The two step selection procedure involved a stratified mass selection system that included check plants for environmental control. In the first step, plants having grain yield higher than 80% of the check-plant mean and protein concentration greater than the check-plant mean were selected. In the second step, the four plants within each selection grid having the highest protein concentration were selected, which resulted in a final selection intensity of 5%, Three cycles of selection were completed during 1991 to 1995. Response to selection was evaluated during the selection process and by direct field evaluation of the C-0, C-1, C-2, and C-3 populations in 1995 and 1996. The average response during the selection was 5.1% cycle(-1) for yield, 0.8 g kg(-1) cycle(-1) for protein concentration, and 7.0% cycle(-1) for protein yield. No measurable differences among cycles were observed in the direct field evaluation even though the trends in the means of the cycles followed the trends shown during selection. After three cycles, the mass selection system studied did not appear to be particularly effective.