Synopsis The formation of floral organs in maize is not prevented by dense planting. Competitive pressure does not produce a marked retardation of ear elongation, ovary development, or silk elongation until approximately 74 days after planting. Barrenness is the result of failure of silk emergence during the pollen‐shedding period.

In 31 inbred lines of maize, which varied widely in Zn concentration of the kernels, the germ (plus embryo), pericarp, and endosperm were found on the average to contain 138, 46, and 9.9 ppm Zn, respectively. The concentration of Zn in each of these kernel components varied widely among the 31 inbreds, however, and the concentration of Zn in the kernel could not be predicted from the relative size of the kernel components. In greenhouse experiments with 32 inbreds, Zn concentration in the kernel was not correlated with Zn uptake by plants or Zn concentration in plants grown on either Zn‐deficient or Zn‐fertilized soil. In field experiments, however, variation among inbred lines in their concentration of Zn in the kernel did appear to be related to the general level of Zn in the plant, but this factor was greatly modified by the extent to which the inbred was able to transfer Zn from the stalk and leaves to the ear. Inbreds Ky211 and Ky209 transferred approximately one‐third of their stalk and leaf Zn to the ear during grain formation. Approximately one‐fourth of the gain in ear Zn from tasseling to maturity by Ky209 × Ky21l could be accounted for by transfer from the stalk and a slight additional amount by transfer from the leaves.

The development of basic breeding populations that are adapted to a wide area and have at least some resistance to crop hazards in a region is important to breeders. A program designed to develop such a population of maize (Zea mays L.) for the northern Cornbelt is described. Six breeders in the area contributed germplasm samples (convergence) which were intercrossed. Samples of the resulting population were sent to each collaborator (divergence) who practiced mass selection for healthy, productive plants. In subsequent years, harvested samples (balanced composites) sent to Wisconsin (the convergent phase) were subdivided and redistributed (divergence) in such a way that seed for each location did not include seed harvested from that location the previous year.Results from the first four cycles of selection were evaluated in performance trials at all locations over a 2‐year period. Significant increases in productivity (gram yield) and reduction in grain moisture at harvest were obtained. Evidence of increased stability was noted over the four cycles of selection.

No abstract