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Several studies have indicated a possible link between genome size and earliness in maize. In this study, an original maize population, South African photo-period insensitive maize composite II (C[SUB0]) and several selected generations were analyzed for days to flowering, plant height, ear height, and yield. The selection criterion was earliness. Over six cycles of selection a 14-day decrease in days to flowering was obtained with no significant reduction in grain yield. In the initial population (C[SUB0]) and the most advanced selection (C[SUB6]) 101 plants were analyzed for nuclear DNA content. A significant decrease in the mean nuclear DNA content of the C[SUB6] population (102 AU) was observed with respect to the C[SUB0] population (105 AU). This reduction was the result of a decrease in frequency of plants in the C[SUB6] population with large genome sizes. Therefore it was concluded that selection for earliness resulted in selection against plants with large genome sizes. Hence, the nucleotype of a maize plant can be modified by selection such as early flowering time. [ABSTRACT FROM AUTHOR]