1. Tetraploidy was induced in
Rauvolfia serpentina (2n=22)-a plant of considerable medicinal importance.
2. Aqueous colchicine solution of two different concentrations viz. 0.25 and 0.5 per cent were applied on cotton wad around stem tip at seedling stage. Both the concentrations responded well to seedling treatment but 9 hrs. treatment with 0.5 per cent gave maximum tetraploids.
3. Colchicine affected shoots were mostly sectorial chimeras, but some were more or less complete tetraploid for all practical purposes.
4. Immediate effects of colchicine on the treated shoots were arrested stem elongation, leading to the enlargement of the treated regions. Tetraploid branches were slow growing and somewhat shorter but sturdier.
5. Leaves were shorter in length but wider, thicker and darker green. The increased thickness was shared both by the palisade and spongy tissues. Stomata were larger and fewer per unit area.
6. Flowering was delayed in the tetraploid plants. Number of flowers per inflorescence was less in the tetraploids and this criterion was quite significant in
Rauvolfia serpentina.
7. The flowers and floral parts showed a marked tendency towards decrease in length, but increase in diameter or width.
8. Change in pollen sterility was found to be invariably associated with induction of tetraploidy. Pollen grains were larger in size with remarkable change in their morphology. Number of apertures varied with the shape. Tetraploid pollen grains were mostly quadrangular or pentangular in shape.
9. Number of fruits and seeds in tetraploid
Rauvolfia plants was significantly reduced.
10. The mean frequency of quadrivalents per cell was 4.8. Irregular distribution, precocious movements, lagging chromosomes and supernumerary spored quartets were seen in
Rauvolfia.
11. Though most of the parts of
Rauvolfia exhibited gigas habit the utility of the tetraploids is yet to be determined by growing the progeny of the tetraploids and estimating the alkaloid contents of the roots of mature plants.
View full abstract