Induction of polyploidy in watermelon

Summary

Several colchicine treatment methods were tried in the varieties Farrukhabadi and Asahi Yamato of watermelon in order to induce chromosome doubling in them. Treatment of seedlings by drop method in the cotyledonary stage with an emulsion comprising 0·2% colchicine, stearic acid, morpholine and lanoline gave the highest percentage of affected plants (38·59%). Next in efficiency was the periodic application of drops of 0·4% colchicine on the growing point. The tetraploids had all the usual characteristics associated with autopolyploidy and during meiosis in a microsporocyte 11 quadrivalents were observed. The mean frequency of quadrivalents per cell was 5·91. Seed fertility in tetraploid watermelon was much reduced and from 4x×2x crosses in Farrukhabadi one fruit containing 67 seeds was obtained. The 3x seeds germinated only when the seed coat was partly removed and the fruit set on a 3x plant had seeds without embryo. There appears to exist genetic variability with regard to the ability of a strain to yield a completely seedless triploid and it is consequently necessary to produce triploids of many varieties and select the desirable ones for the commercial production of seedless watermelon.