A new method for producing seedless watermelon ( Citrullus lanatus ) in diploid plants using soft-X-irradiated pollen is described. Fruit set at almost the same rate despite soft-X-irradiation. Empty seeds were produced in the watermelon cultivars ‘Benikodama’ and ‘Fujihikari TR’ following hand pollination using soft-X-irradiated pollen. Soft-X-irradiation doses of 800–1000 Gy resulted in small empty seeds in ‘Fujihikari TR’, whereas 400–1000 Gy doses gave the best results for ‘Benikodama’, although empty seeds in the latter were many and conspicuous. Soft-X-ray treatments did not affect fruit weight, shape, rind thickness or days to maturation compared to controls. However, female flowers treated with soft-X-irradiated pollen produced fruits with slightly higher sugar content compared to controls in ‘Benikodama’. Therefore, this new method is an effective technique to produce seedless watermelon.
