Imidazolinones, Bromoxynil, and Glufosinate resistance in plants develops through specific genetic transformations introducing bacterial genes that detoxify or bypass herbicide action. The correct matching identifies Imidazolinones with acetolactate synthetase resistance, Bromoxynil with nitrilase, and Glufosinate with phosphinothricin acetyltransferase. Option (A) P-2; Q-1; R-4 provides the accurate pairing based on established biotechnology mechanisms.​

Correct Answer

Option (A) correctly matches the herbicides to their resistance modes: P (Imidazolinones)-2, Q (Bromoxynil)-1, and R (Glufosinate)-4. Imidazolinones target acetolactate synthase (ALS), inhibited in susceptible plants; resistance via transformation with a resistant ALS version prevents binding. Bromoxynil resistance uses bacterial nitrilase to hydrolyze the nitrile group into non-toxic forms, while Glufosinate resistance employs the bar gene from Streptomyces hygroscopicus encoding phosphinothricin acetyltransferase (PAT) to acetylate and detoxify the active compound.​

Imidazolinones Resistance (P-2)

Imidazolinones inhibit ALS enzyme crucial for branched-chain amino acid synthesis in plants. Resistance develops by transforming plants with a mutated, herbicide-insensitive ALS gene, allowing normal enzyme function despite herbicide presence. This target-site resistance is widely used in crops like canola and mustard varieties.​

Bromoxynil Resistance (Q-1)

Bromoxynil, a nitrile herbicide, disrupts photosynthesis by binding photosystem II. Plants gain resistance through bacterial nitrilase gene transformation, which breaks down the nitrile to cyanobromide and benzoic acid, non-phytotoxic products. This metabolic detoxification enables selective herbicide use in resistant crops.​

Glufosinate Resistance (R-4)

Glufosinate inhibits glutamine synthetase, causing ammonia accumulation and plant death. The bar gene from Streptomyces hygroscopicus encodes PAT, which N-acetylates glufosinate into inactive N-acetylglufosinate, conferring resistance. LibertyLink crops exemplify this mechanism, though expression levels influence efficacy.​

Incorrect Options Explained

• Option (B) P-2; Q-1; R-3: Wrongly assigns tfdA gene (for 2,4-D degradation via dioxygenase) to Glufosinate; tfdA targets phenoxy herbicides, not phosphinothricins.​

• Option (C) P-1; Q-2; R-3: Misplaces nitrilase (Bromoxynil) to Imidazolinones and ALS to Bromoxynil, inverting ALS inhibitors with nitrile detoxifiers.​

• Option (D) P-4; Q-1; R-3: Errs by linking bar/PAT (Glufosinate) to Imidazolinones and tfdA to Glufosinate, confusing unrelated metabolic pathways.​