Growth and flowering of black iris ( Iris nigricans Dinsm.) following treatment with plant growth regulators

Abstract

The effects of application method and concentration of gibberellic acid (GA 3), paclobutrazol and chlormequat on black iris performance were assessed. Plants (10 cm high, 4 ± 1 leaves) were sprayed with 125, 250, 375 or 500 mg L −1 or drenched with 0.25, 0.5, 1 or 2 mg L −1 GA 3. In a second experiment, the plants were sprayed with 100, 250, 500 or 1000 mg L −1 or drenched with 0.25, 0.5, 1 or 2 mg L −1 paclobutrazol. Other plants were sprayed with 250, 500, 1000 or 1500 mg L −1 or drenched with 100, 250, 375 or 550 mg L −1 chlormequat. In each experiment, the control treatment consisted of untreated plants. Results indicated that the tallest plants (37.3 cm) in the GA 3 experiment were those sprayed with 250 mg L −1. The most rapid flowering (160 days after planting) occurred when a 375 mg L −1 GA 3 spray was used, whereas flowering was delayed to 200 days using 1 mg L −1 GA 3 drench. Drenching with 1 mg L −1 GA 3 increased height of the flower stalk by 7 cm compared to the control. Though relatively slow to flower, plants drenched with 1 mg L −1 GA 3 had long and rigid stalks, which were suitable as cut flowers. Number and characteristics of the sprouts were not affected by GA 3. All paclobutrazol sprays resulted in leaf falcation. A 500 or 1000 mg L −1 paclobutrazol spray resulted in severe and undesirable control of plant height, drastic reduction in stalk height and weight, and delayed flowering. Plants drenched with 0.25 or 1 mg L −1 paclobutrazol were suitable as pot plants. Chlormequat reduced plant height only at the highest drench concentration, which also reduced flowering to 70%. No leaf falcation was observed with GA 3 or chlormequat. Chemical names: ( ± )-( R*, R*)-beta-((4-chlorophenyl)methyl)-alpha-(1,1,-dimethylethyl)-1H-1,2,4,-triazol-1-ethanol (paclobutrazol); (2-chloroethyl) trimethylammonium chloride (chlormequat).