Development of seedless berries in some cultivars increases as the ploidy level increases from diploid to tetraploid. Effect of the ploidy level on parthenocarpic berry formation was investigated with three pollination treatments (non-pollination, pollination with sterile pollen of a triploid hybrid and open pollination) in eight diploid and four tetraploid cultivars. In non-pollination, 'Italia', 'Rosario Bianco', and 'Yufu' showed vegetative parthenocarpy and produced seedless berries, with rates of 39.1, 23.3, and 72.1%, respectively. Pollination with sterile pollen of a triploid plant induced stimulative parthenocarpy in all cultivars except 'Rozaki'. 'Italia', 'Muscat Bailey A', 'Rosario Bianco', 'Delaware' and 'Muscat of Alexandria' showed a high degree of stimulative parthenocarpy, whereas 'Neo-Muscat' and 'Sekirei' a showed very low degree. 'Cannon Hall Muscat' and 'Red Pearl', in comparison with their original diploid forms, showed relatively high fruit set rates when pollinated with the sterile pollen. In open pollination, the rates of parthenocarpic seedless berries were low in most cultivars except for 'Cannon Hall Muscat', 'Yufu', and 'Red Pearl'. 'Yufu', a tetraploid form of 'Muscat Bailey A', showed the high parthenocarpic berry production rates in all the three treatments. These results suggested that increasing of ploidy levels increases parthenocarpy in the thinly parthenocarpic diploids, and among the cultivars used, 'Rosario Bianco' has the highest parthenocarpic ability resulting in about 4 g of seedless berries and the high rate of fruit set.
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