Evaluation of Exotic Germ Plasm for Improving Corn Hybrids in Northern United States 1

Thirty‐six synthetic lines of corn ( Zea mays L.) derived from crosses between 12 New York hybrids and bulked lots of exotic pollen were studied. The synthetics were divided into three groups: M—originated from crosses with multiple races of maize; C—from crosses with maizeteosinte admixture selected to be maize‐like; T—from crosses with maize‐teosinte admixture selected to be teosinte‐like. Results of this study indicated that the M, C, and T groups differed in the number of chromosome knobs, number of kernel rows, and time of maturity. Introduction oil an increased amount of teosinte germ plasm resulted in earlier maturing plants with higher content of dry matter in the stover and grain, but with vegetatively less vigorous plants. In top crosses with four testers, the synthetics yielded significantly less grain than the controls, but were excellent in vegetative growth. New York hybrids were significantly different in their combining ability with the exotic germ plasm. Significant correlation coefficients were found between chromosome knob numbers anti seven variables as studied in top crosses.