Observations on Sterility of Induced Autotetraploid Watermelons1

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Abstract
Autotetraploid watermelons were produced by treating the growing points of diploid seedlings with aqueous colchicine solution or by soaking diploid seeds in colchicine solution. The soaking method was more effective. Diploid pollen was apparently more viable than tetra-ploid pollen. Examination of germinating tetraploid pollen revealed that while over two-thirds germinated normally a small percentage sent forth 2, 3 or 4 normalsized pollen tubes or a single bifurcated tube. Germinating diploid pollen always put forth only one unbranched pollen tube. Tetraploid plants did not set fruit when pollinated with pollen from tetraploids; however, they did set fruit when pollinated with pollen from diploids. Cytological observations were made of pollen mother cells of both diploid and tetraploid plants. Meiosis in diploids was regular; however, irregularities were observed in tetraploids. Examination of some pollen mother cells of tetraploids at the quartette stage revealed micro sporocytes in addition to the 4 microspores. The abnormal quartette formations and lower pollen viability of tetraploids were believed associated with irregularities observed at meiosis. Preliminary investigations of megaspore formation revealed no apparent differences between the diploid and tetraploid megaspores. Although meiotic irregularities were found, a sufficient amount of apparently viable pollen was observed. A physiological basis for the self-sterility is suggested.

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