Induction of polyploidy in two diploid wild cotton ( G . armourianum and G . aridum ) species by colchicine treatment

In cotton, wild species generally have in built in resistance of desirable genes for biotic and abiotic stresses and possessing useful fibre qualities such as high length and strength. Among the antimitotic agent, colchicine is widely used to induce doubling of the chromosomes in plant species. Attempt has been made to increase the ploidy level in two wild cotton species viz. (G. armourianum, L and G. aridum) to make crosses with tetraploid G. hirsutum, L cotton. A dose dependent increase in ploidy level was observed. Significant difference was noticed in induction of polyploidy and plant growth rate that depends on dose of colchicine, duration of the treatments and type of plant material have been observed in the study. Increase in the concentration of colchicine or duration of the treatment showed negative effects on seed viability in both the species under study. The colchicine treatment is more effective when the length of hypocotyls is between 4 8 mm. The root meristem of G. armourianum, L treated with 0.7% colchicine exhibited more tetraploid cells in 20 hrs treatment. The increase in the concentration of colchicine with increase in duration leads chromosomal abnormalities in both the wild species. Among the three methods employed in inducing polyploidy in wild diploid cotton, seed treatment was more efficient and reliable as compared to other seedling and cuttings treatments.