Plant Growth and Development

The 'bakanae' or 'foolish seedling' disease of rice had been known in Japan since the early 1800s.
The diseased rice plants were thin, pale green and spindle-shaped, longer by about 50 percent than the healthy plants, and were sterile.
The disease is caused by the fungal pathogen Gibberella fujikuroi.
E. Kurosawa (1926) showed that the symptoms appeared in healthy rice seedlings when they were treated with sterile filtrates of the fungus.
The active substance was later identified as gibberellic acid (GA).
ABA is a growth inhibitor, IAA is a natural auxin (discovered through experiments on coleoptile curvature) and 2,4-D is a synthetic auxin used as a herbicide.
So the foolish seedling disease of rice led to the discovery of GA (gibberellins).

Gibberellic acid stimulates the growth of stems and leaves, causing elongation of internodes and expansion of leaves; it also breaks dormancy, causes bolting and delays senescence.
Leaf fall (abscission) is not caused by gibberellic acid; it is promoted by abscisic acid (ABA) and ethylene. So the pair gibberellic acid - leaf fall is not correctly matched.
Cytokinins promote cell division (cytokinesis).
IAA (indole-3-acetic acid, an auxin) causes cell elongation by loosening the cell wall.
Abscisic acid stimulates the closure of stomata during water stress, and is therefore called the stress hormone.
So the pair that is not correctly matched is gibberellic acid - leaf fall.