Q.49. 2-Methoxy-3, 6-dichlorobenzoic acid belongs to which class of plant growth regulators?
(A) Synthetic auxin
(B) Synthetic cytokinin
(C) Strigolactone
(D) Brassinosteroid
2-Methoxy-3,6-dichlorobenzoic acid, commonly known as Dicamba, functions as a synthetic auxin herbicide and plant growth regulator. The correct answer to the MCQ is (A) Synthetic auxin.
Compound Identification
This chemical, with the formula C8H6Cl2O3, mimics natural auxins like indole-3-acetic acid (IAA) to disrupt plant growth in weeds. Dicamba belongs to the benzoic acid herbicide family and acts systemically, absorbed by leaves and roots.
Correct Answer Explanation
Option (A) Synthetic auxin fits because Dicamba promotes excessive cell elongation and vascular tissue growth, leading to uncontrolled development and plant death in susceptible species. Classified as a synthetic auxin, it targets broadleaf weeds effectively in crops like soybeans.
Option Breakdown
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(A) Synthetic auxin: Correct; Dicamba structurally resembles IAA and binds auxin receptors, causing hormonal imbalance.
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(B) Synthetic cytokinin: Incorrect; cytokinins like benzylaminopurine promote cell division and delay senescence, unlike Dicamba’s elongation effects.
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(C) Strigolactone: Incorrect; these natural compounds regulate shoot branching and stimulate mycorrhizal fungi or parasitic plants, unrelated to benzoic acids.
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(D) Brassinosteroid: Incorrect; brassinosteroids enhance stem elongation and stress tolerance via distinct steroid pathways, not matching Dicamba’s profile.
Agricultural Applications
Farmers apply Dicamba in formulations for post-emergence weed control, often with glyphosate in GMO crops resistant to it. Its potassium salt form enhances solubility as a growth regulator. Understanding these classes aids agronomy students and professionals in precise herbicide selection.
