Maximum amount of growth in roots occurs due to

Which of the following auxins is widely used as a weedicide?

Apical dominance is caused by

In botanical gardens and tea gardens,gardeners trim the plants regularly so that they remain bushy. Does this practice have any scientific explanation?

$A$ : Auxin treatment causes acidification of the cell wall and helps in cell elongation.
$R$ : Loosening of cell wall microfibrils occurs.

The substances which have proved very effective to induce rooting from the cut end of the stem are: