In vitro culture of three parts of watermelon seedling was carried our on 20 modified MS media. The cotyledonous tissue was induced to produce callus, root and shot. Three types of callus, were found. The translucent white callus was formed on the cotyledon surface in almost every medium formular used. The yellowish callus grew from cutsurface of the cotyledonous tissue in the media MS+1-2 mg/1 IAA+10 mg/1 BAP and could differentiate into a shoot in medium MS+1 mg/1 IAA +10 mg/1 BAP. Root formation from cotyledonous tissue was found in the media MS+1-2 mg/1 IAA or NAA without BAP. Although less number of root was produced but better growth of root was found in the medium containing of root was found in the medium containing ANN. Two types of callus : yellowish and greenish were produced from the hypocotyls However, formation of white callus, shoot and root were found in Hypocotyls culture. In shoot tip culture, the shoot grew, elongated and rooted best in the medium MS+ IAA 1 mg/1. Polyploid induction of watermelon in different concentration of colchicines; 0.5, 0.1, 0.05 and 0.01% in water and in liquid culture medium MS treated 12, 24 and 48 hours were studied from the size of guard cell, number of chloroplast, root length and chromosome number. As a result, watermelon plantlets treated with 0.05% colchicines solution for 12 hours, liquid medium MS +0.05% colchicines for 12 hours, liquid medium MS+0.05% colchicines for 12 hours, liquid medium MS+0.05% colchicines for 24 hours and liquid medium MS+0.01% colchicines for 12 hours, showed statistical difference in size of guard cells and number of chloroplast but root length has no significant difference to the control. The technique of cell preparation from in vitro watermelon root tip for chromosome number study is not successful in this experiment.
