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Spikelet Abscission in Guineagrass as Influenced by Auxin and Gibberellin¹

Seed production of guineagrass (Panicum maximum Jacq.), an important pasture and forage crop in the tropics, is hindered by its heavy loss of seeds through spikelet abscission. A method whereby abscission could be delayed or arrested would be a great aid in seed harvest of this and other Panicum species.

Auxin and gibberellin at three concentrations (10-3, 5x10-3 and 10-2M) were applied to the inflorescences of two experimental genotypes (PM285 and 68s-5-2) when the panicle was three-fourths emerged from the flag leaf to inhibit spikelet abscission. Growth chamber and field experiments were conducted.

Response was dependent on plant genotype and growth regulator concentration. In the growth chamber, panicle branch explants were inserted into semisolid agar solutions of growth regulators. The most responsive auxin treatment inhibited abscission by 32%. In the field, aqueous sprays of growth regulators were app.lied to entire inflorescences. The most responsive auxin treatment inhibited abscission by 40%, The two genotypes responded differently to IAA treatment with 68s-5-2 exhibiting significantly less abscission than PM285. Gibberellin treatments either stimulated abscission or had no influence under the conditions tested.

Histological sections of pedicels of the genotype 68s-5-2 were made to follow the development of the abscission zone with and without applied auxin. The abscission zone exhibited no readily observable morphologlc or histologic response to auxin.

Key Words: Seed yields • Seed shatter • Plant growth regulators

² Gradnate research assistant, professor and assistant research scientist, respectively, Agrouomy Dep., Univ, of Florida, Gainesville.

Received for publication April 24, 1978.