Abstract: The experiments for increasing the induction frequency of tetraploid watermelon were made with three methods of colchicine treatment, with 6 diploid varieties of watermelon as materials. When the small leaves were peeled off and the bare growth tips were treated with colchicine drops, the variation frequency (the number of variated plants/the number of suvival plants) was 52%, and the treatment efficiency (the number of variated plants/the number of treated plants) was 30.4%. When the bare growth tips were daubed with Lanolin paste mixed with colchicine, the variation frequency and treatment efficiency were 61% and 29.4%, respectively. When the growth tips were covered with small leaves they were immersedinto colchicine solution, the variation frequency and treatment efficiency were 39.1 % and 23.7%, respectively. The mentioned methods were much better than the conventional methods.

Key words: Watermelon, Tetraploid, Induction frequency