Gibberellic Acid‐controlled Sex Expression of Corn Tassels1

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Abstract
Foliage of corn (Zea mays L.) was sprayed with gibberellic acid (GA3) in an attempt to regulate sex expression of corn tassels. Complete suppression of staminate development would facilitate hybrid seed production. Tassels of inbred lines ‘A619’ and ‘Gaspd Flint’ became pistillate, male sterile, or remained male fertile depending on the time of GA3 application. Maximum pistil development within the tassel occurred when 5 mg/plant of GA3 was applied 8 or 9 days prior to the start of microspore meiosis. Complete male sterility without pistil development was observed when applications were made 1 to 3 days before the onset of meiosis. Sex expression of the tassel was not altered when GA3 treatments were made after the start of meiosis. Ear sex expression was not modified by any of the treatments. Stem weakness accompanied pistillate expression within the tassel and the stem either broke or was incapable of holding the plant in a verticle position. GA3 treatments altered stem and peduncle elongation but did not change total plant height. The precise timing needed to obtain male sterility without stem weakness reduces the utility of GA3 for hybridizing large populations. Plants in a normal field population do not reach this time frame at an uniform rate.

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