Growth and reproductive development of alfalfa as influenced by 2,3,5-triiodobenzoic acid

Abstract

The plant regulator 2,3,5-triiodobenzoic acid (TIBA) at concentrations of 0, 10,50, 100, or200 ppm(0, 2 × 10−5, 1 × 10−4, 2 × 10−4,or4 × 10−4 M, respectively) was applied to leaves of alfalfa grown at 14-h day length, 12 000 μW cm−2, 20 °C day–16 °C night. The number of racemes per primary stem and on axillary branches was recorded daily for 34 days after TIBA application. Length of primary stems and branches and number of nodes and branches were determined 34 days after TIBA application.TIBA did not affect number of nodes or branches per primary stem, but at a concentration of 10 ppm it promoted the elongation of both primary stems and axillary branches and also raceme formation on both stems and branches. This resulted in a fivefold increase in total branch length per primary stem and a highly significant increase in total raceme production. These results may explain in part reported effects of TIBA on seed production of alfalfa and are also consistent with reported effects of TIBA on flowering and axillary bud development in several other legumes.The observation that two structures (branches and (or) racemes) may typically arise from an alfalfa leaf axil may be useful in understanding the phenomena of branching and floral initiation in this crop.