Seedless Fruit Formation and Dry Matter Partitioning in Medium-fruit Sweet Pepper ‘Papriko’, and Effects of Plant Growth Regulators on Fruit Development

Abstract

Yield fluctuation, a significant challenge in sweet pepper production, is likely related to suppression of flower development and the fruit set ratio due to competition from dominant fruits with strong fruit sink strength. First, we examined the effect of pollinated or unpollinated (stigma removed before anthesis) treatments on fruit development and dry matter partitioning in the medium-fruit sweet pepper ‘Papriko’, with two levels of fruit load in an unheated greenhouse setting. With the unpollinated treatment, the fruit set ratio was lower than that in the pollinated treatment, and the fruit weight was 60–70% of that of the pollinated fruit, regardless of the fruit load. In the pollinated treatment, the dry matter weights of leaf blades, petioles, and stems decreased, whereas in the unpollinated treatment, stem and leaf weights did not decrease. The incidence of blossom-end rot in fruits was higher in pollinated plants. Second, we sprayed the stigma-removed flowers with parachlorophenoxyacetic acid (PCPA) and forchlorfenuron (FCF) as plant growth regulators to achieve more stable parthenocarpic fruit growth. The fruit set ratio and fruit fresh weight post 30 ppm PCPA treatment were lower than those after the pollination treatment. Spray treatment (30 ppm PCPA and 100 ppm FCF) induced parthenocarpic fruit with 70% of the weight of pollinated fruit, and an intermediate fruit set ratio between that in the non-pollinated and pollinated plants. FCF tended to increase mesocarp cell numbers and thicken the pulp. Parthenocarpic fruits contain high levels of ascorbic acid. Finally, spray treatment with 30 ppm PCPA and 100 ppm FCF at anthesis without stigma removal suppressed seed formation and induced parthenocarpic fruit formation. These results suggest that parthenocarpy effectively reduces harvest fluctuations by decreasing dry matter competition and controlling fruit sink strength.