Q.54. Which of the following chemicals is used for doubling of chromosome numbers during production
of ‘doubled haploids’ in crop plants?
(A) Hygromycin
(B) Kanamycin
(C) Colchicine
(D) Glufosinate
Colchicine is the chemical used for doubling chromosome numbers during doubled haploid production in crop plants. This process accelerates breeding by creating homozygous lines rapidly.
Correct Answer
** (C) Colchicine **
Colchicine binds to tubulin, disrupting spindle fiber formation and preventing chromosome separation during mitosis, which results in cells with doubled chromosomes. In doubled haploid production, haploid plants or embryos from anther culture or gynogenesis are treated with colchicine solutions (typically 0.1-0.5%) to generate fertile doubled haploids for breeding programs in crops like wheat, maize, and barley.
Option Explanations
| Option | Chemical | Role in Plant Biotechnology | Why Not for Chromosome Doubling? |
|---|---|---|---|
| (A) | Hygromycin | Aminoglycoside antibiotic used as a selectable marker in plant transformation to kill non-transgenic cells. | Inhibits protein synthesis; no effect on microtubules or mitosis. |
| (B) | Kanamycin | Aminoglycoside antibiotic serving as a selectable marker in genetic engineering for transgenic plant selection. | Targets bacterial-like ribosomes in plants; does not induce polyploidy. |
| (C) | Colchicine | Mitotic inhibitor that blocks spindle formation, causing chromosome doubling in haploids. | Correct choice, widely used in DH protocols. |
| (D) | Glufosinate | Herbicide and selectable marker (bar gene) that inhibits glutamine synthetase in non-resistant plants. | Causes cell death via ammonia accumulation; unrelated to chromosome manipulation. |
Doubled Haploids in Crop Breeding
Doubled haploids (DH) are completely homozygous plants derived from haploids (n chromosomes) by doubling to 2n, enabling rapid fixation of traits without selfing generations. Techniques involve colchicine treatment on haploid seedlings or embryos, with success rates optimized by concentration, duration, and additives like DMSO. This method shortens breeding cycles from 10-12 years to 2-3 years in crops like wheat.
