328 



Colchicine 



loids causes iruit development among triploids. However, the ste- 

 rility of the female precludes seed setting even though viable diploid 

 pollen is present. This is the general scheme in producing triploid 

 watermelons that under specific circumstances set seedless fruits. 



The general procedure of formation of triploid fruits is set forth 

 diagrammatically in Figure 13.1. Only crosses involving the female 



2x X 4x 4x X 2x 



i 



2x 



empty 

 seeds 





Fig. 13.1 — Triploid watermelon. Propagation of triploid seed by crossing diploid and 



tetraploid lines. Use of colchicine to make tetraploid stocks. Fruits from diploid, 



triploid, and tetraploid stocks. (Adapted from Kihara) 



as tetraploid and the male as diploid pollinator are successful. Re- 

 ciprocal procedures do not succeed. 



As in autotetraploids, the size of flowers increases in proportion to 

 the increase in chromosome number. This relation holds for tetra- 

 ploid pollen and stomata. Triploid pollen is variable in size and can- 

 not be made to fit the proportional increase as chromosome numbers 

 increase. Many grains are empty while others are full and may be 

 huge. 



The 3X seed is a tetraploid seed with triploid embryos obtained 

 from a diploid pollination. The SX seeds are slightly thinner, averag- 



