Auxin-gibberellin interaction in apical dominance: Experiments with tall and dwarf varieties of pea and bean.

Seedlings of dwarf and tall varieties of pea and bean, growing in John Innes Compost No. 2, were studied in relation to the effects of decapitation, indole-3-acetic acid (IAA), and gibberellic acid (GA3) on axillary bud growth. In all varieties, GA3 antagonized the inhibitory influence of IAA on bud growth when both hormones were applied to the upper cut end of the stem. Thus, GA3 caused a reduction in IAA-induced correlative bud inhibition in tall, as well as in dwarf, plants. These results agree with those obtained by several workers, but contrast with some recent reports of increased apical dominance in a tall pea variety when seedlings were treated with GA3 in addition to IAA. An attempt was made to identify the cause of opposite results being obtained by different workers, and it is considered that possibly the most important factor is mineral nutrition.