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Root development is promoted by
A
Abscisic acid
B
Auxin
C
Gibberellin
D
Ethylene
Detailed Solution
NCERT, under ethylene, states: 'Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface.'
On this basis the answer accepted in the key is ethylene.
Abscisic acid is a growth inhibitor, and gibberellins promote stem elongation and bolting rather than root development.
Note: auxin is also known to help initiate rooting in stem cuttings (NCERT), so 'auxin' is given as the answer in some books; the key of the source PDF (ethylene) is retained here.
On this basis the answer accepted in the key is ethylene.
Abscisic acid is a growth inhibitor, and gibberellins promote stem elongation and bolting rather than root development.
Note: auxin is also known to help initiate rooting in stem cuttings (NCERT), so 'auxin' is given as the answer in some books; the key of the source PDF (ethylene) is retained here.