Recurrent Selection for Cold Temperature Seedling Growth in Sweet Corn.

In Wisconsin, the race to get the first sweet corn to market always depends on the soil temperature. Most sweet corn cultivars don’t germinate well at cold temperatures. Recurrent selection was carried out in three sweet corn populations with the intention of increasing seedling vigor and germination rates at cold temperatures. The original populations were formed by crosses of temperate sweet corn with exotic Mexican germplasm native to high altitudes. A sugary1 (su1) and a shrunken2 (sh2) population derived from ‘Cacahuacintle Dulce’ were evaluated, as well as a sh2 population derived from ‘Maíz Dulce’. The sh2 populations have undergone four cycles of selection while the su1 population has undergone five. Each cycle was formed through replicated visual selection of the most uniformly vigorous seedlings. The direct effects of selection were measured through growth chamber germination tests at 11°C. The indirect effects of selection were assessed through kernel carbohydrate analysis, dry kernel weights, and phenotypic analysis of the plants in replicated field trials. The seedling length and number of live kernels was significantly improved over cycles of selection in both sh2 populations, while progress was not detected in the su1 population. The ‘Cacahuacintle Dulce’ sh2 and ‘Maíz Dulce’ sh2 populations saw a 42% and 51% increase in seedling length over cycles, respectively. The ‘Maíz Dulce’ sh2 population had a cycle zero (C0) mean of 59% germination. At cycle four (C4), the same population had a mean of 83% germination.  While germination under field conditions improved for both of the sh2 populations, yield had a tendency to decrease over cycles of selection. The ‘Cacahuacintle Dulce’ su1 population saw the largest decrease in mean yield at 26% from C0 to C5.