Effects of divergent selection for endosperm appearance in a Sugary1 maize popuiation

The characteristics of sweet corn endosperm are due to alleles that disrupt normal starch synthesis. Changes in carbohydrate synthesis in sweet corn induced by phenotypic selection may result in information useful in understanding normal starch synthesis. A maize population homozygous for the sugary1 (su1) allele underwent three cycles of divergent recurrent selection for either pseudostarchy endosperm or extreme sugary endosperm. The resultant seven populations were evaluated for plant, ear, and kernel characteristics in replicated trials in four environments. Divergent selection for endosperm appearance was successful. Selection for endosperm appearance also resulted in a number of significant indirect responses, some linear and highly correlated to cycles of selection, others non-linear, perhaps due to drift. Cold germination, pericarp injury, and starch and sugar content all changed significantly in predictable directions and were highly correlated with cycles of selection. Kernel weight increased in the pseudostarchy direction and decreased in the sugary direction, however yield was unaffected by selection. The change in kernel weight did not affect yield because other yield components, kernel row number, ear length, and ear diameter, changed in response to selection. Endosperin appearance and number of red cobs in the population were strongly correlated (r = -0.98). The change in the number of red cobs was due to a change in the frequency of alleles at pi, the cob color gene. The direct target of selection, endosperm appearance, is probably controlled by multiple genes. But, it appears that a gene or genes involved in starch synthesis or a correlated trait such as kernel row number is linked to p1 on chromosome 1.