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Response of Soybeans to Amo-1618 and Photoperiod¹

Segregating populations from two soybean (Glycine max (L.) Merr.) crosses were sprayed with aqueous solutons of 0, 250, 500, 1,000, and 2,000 ppm (4-hydroxy.5-isopropyl-2-methylphenyl)trimethylammonium chloride I. lpiperidinecarboxylate, designated Amo-1618. Treatments were applied at V2 (when the first trifoliolate unrolled) and again at V3 (when the second trifoliolate unrolled) on plants grown under 12, 14, and 16-hour photoperiods in the greenhouse. A concentration of 250 ppm reduced plant height to an average of 76% of the untreated control under 12-hour photoperiods, 64% under 14-hour photoperiods, and 66% under 16-hour photoperiods. A concentration of 500 ppm, applied only at V2, reduced plant height to 50% of the untreated control under a 12-hour and 62% under a 14-hour photoperiod. The same concentration, applied again at V3, resulted in an additional decrease in height. Concentrations of 250 ppm nnder a 12-hour or of 500 ppm under a 14-hour photoperiod, sprayed ou plants at V2 and again at V3, resulted in plants 20 to 30 on tall compared to untreated plants that were 39 to 56 cm tall. This was a convenient plant size to advance large, segregating populations in the greenhouse with a mnimum of maintenance.

Key Words: Growth retardant • Single-seed descent

² Research Geneticist, USDA, and Professor of Agronomy, Purdue University, W. Lafayette, IN 47907.

Received for publication March 4, 1974.