Morphology, physiology and environmental effects of triploid watermelon seed germination

Abstract

Triploid or seedless watermelon (Citrullus lanatus (Thunb.) Matsum and Nakai), production and consumption has been increasing rapidly. In 1997 it was estimated that in the year 2000 more than half of the watermelon US production and sales would be from seedless. The largest problems with growing seedless watermelons are poor, inconsistent germination, and the high cost of seed. Research on understanding or improving triploid seed germination has been limited. This research takes a three-part approach to the problem. First, the morphology of the seed coat was examined. In the morphology section, scanning electron microscopy (SEM) was used to determine the basic structural differences in the seed coat. Seed components characteristics were also measured. Secondly, total protein amounts (ug/mg) and specific sugars in dry and germinating diploid and triploid seeds were measured. Finally, control and nicked diploid and triploid seeds were placed under different environmental conditions. Understanding differences in the morphology, physiology and environmental effects of triploid and diploid watermelon will provide critical information to develop techniques to improve germination. In conclusion, SEM micrographs showed a difference in the endotesta of the seed coat and cotyledon arrangement within the seed coat. There was large variability in seed coat thickness of the triploids as compared to diploids. The air space or seed cavity in a nongerminated triploid seed was also greater and more variable than that of a germinated triploid seed. There appeared to be a high level of total soluble protein in the triploid seeds as compared to the diploids, a difference also detected between the high and low germination lots of the triploids. Raffinose appeared to be present after imbibition in the low germination lot, while raffinose was absent in high germinated lots of triploids. The triploid seeds were also more sensitive to high moisture conditions compared to diploid. Further research proposed includes the development of seed priming treatments, such as solid matrix priming, and determining the effects of environmental factors during seed development, and genetic studies investigating morphological and physiological markers in the tetraploid and diploid parents used to make triploid plants.