Seed abortion of ‘Tosa-Buntan’ pummelo pollinated with soft-X-irradiated pollens

Cross-pollination was performed with soft-X-irradiated hyuga-natsu pollens (1000 Gy) for ‘Tosa-Buntan’ pummelo (Citrus grandis (L.) Osbeck). This resulted in the transformation of large and complete seeds into small and empty ones (practically seedless). Although fruit set, fruit retention, total soluble solids content (TSS) and titratable acidity of the juice were not affected, decrement in the fruit size was observed. Two weeks after the pollination, endosperm cell division with free nuclei began in both the non-irradiated and irradiated pollen treatment conditions. Seven weeks after pollination, endosperm division with the cell wall occurred in the non-irradiated pollen treatment conditions; however, the endosperm development ceased in most ovules that underwent the irradiated pollen treatment, and the ovules remained in their free nuclear stage. The delayed degeneration of the ovules, following successful fertilization and commencement of endosperm cell division, allow these seedless fruits to be categorized as pseudo-parthenocarpic.