**Present address: Biology Division, Atomic Energy Establishment, Trombay, Bombay.
*A part of the thesis submitted by the senior author to the P.G. School, I.A.R.I. New Delhi, for the award of Ph.D. degree in Horticulture.
Several methods of colchicine treatment were tried in grapes and tetraploidy successfully induced in eleven out of the thirteen varieties tried. Seedling and bud treatment gave positive results while seed and whole short treatment were ineffective. Three application of 0.2 per cent. colchicine at cotyledonary stage on alternate days have been found to be effective. Treatment of axillary buds with 0.25 and 0.50 per cent. colchicine in 5 per cent. glycerine on alternate days for three days was found to be best. Although varying success was obtained with different varieties, a maximum of 29.1 per cent. tetraploid was obtained in the variety Beauty Seedless with 0.50 per cent colchicine in 5 per cent glycerine. A comparison of freshly rooted cuttings and one or two year old rooted cuttings showed that the latter were more suitable for treatment.
Both pre-(active growth of buds) and post-colchicine treatments (active growth as well as removal of unwanted and unaffected growths to reduce the extent of intrasomatic selection) have been found to be important considerations for ensuring success of the treatments. Induced tetraploids showed many diagnostic features like vigorous growth, thick and deeper coloured leaves with increased leaf area and serrations, short and stout internodes, tendrils, etc, which were helpful in the detection, confirmation and isolation of tetraploid shoots.
