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Response of Prolific and Nonprolific Maize to Growth-Regulating Chemicals

In two different experiments, three prolific and three nonproliflc single-cross hybrids of maize (Zea mays L) growth were treated with growing regulating chemicals to determine their effects on ear development. In experiment A, the compounds used were N-l-naphthylphthalamic acid (NPA), p-chlorophenoxyisobutyric acid (PCIB), and 6-(-dimethylalllyamino) purine (i⁶Ade), all at concentration of 10-⁴M. Treatments were applied as 0.5-ml injections to the internode between the first and second ear shoots of nonprolific hybrids and between the second and third ear shoots of prolific hybrids. The auxin translocation inhibitor (NPA) significantly increased total yield of nonprolific hybrids and increased lower ear grain weight and ear number of all hybrids. The antiauxin, PCIB, had no discernible effect, while i₆Ade (cytokinin) treatments decreased total yield of nonprolific hybrids and the yield of lower ears of all hybrids. In experiment B, upper ear shoots were excised on the day of silking and treatments of indolebutyric acid (IBA), gibberellic acid (GA₃), and cytoklnin (PAde) were injected into the remaining ear shank. Gibberellic acid and combinations of IBA and GA₃ treatments sgnificantly reduced ear number. The results of these experiments indicate that indoleacetic acid (IAA), GAa, and possibly other hormones interact in a time-dependent mode to inhibit lower ear development. The close relationship between sink size and total yield demonstrates the importance of an adequate sink for plants grown at low density.

Key Words: Prolificacy • Apical dominance • Plant hormes • Zea mays L.

² Postdoctoral fellow, Dep. of Agronomy, Univ. of Wisconsin-Madison; assistant professor, Dep. of Preventive Medicine and Public Health, Creighton Univ., Omaha, NE 68178; and professor, Dep. of Agronomy, Madison, respectively.

Received for publication December 23, 1977.